Patent Publication Number: US-2009231107-A1

Title: Testing device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2008-068172, filed on Mar. 17, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments discussed herein are directed to a testing device for testing the performance of an electronic device that receives and reacts to a predetermined radio signal and a testing method of such a performance testing. 
     BACKGROUND 
     In recent years, various types of RFID (Radio Frequency Identification) tags, which perform noncontact exchange of information with external devices represented by a reader/writer through radio waves, have attracted attention. A type of the RFID tags has been proposed, the RFID tag being mounted with antenna patterns and IC chips for radio communication on a base sheet made of plastic or paper. Such a type of RFID tag is attached to commodities and the like and can be used for exchanging information related to the commodities with external devices to identify the commodities. A system utilizing the RFID tag is implemented or examined in every field such as agriculture, fishery, manufacturing, distribution, services, medical, welfare, public, government, traffic, and transportation. 
     One of the main performances of such an RFID tag is a communication limit distance equivalent to a maximum distance in which communication with an external device that transmits a radio signal with a predetermined output is possible. The communication limit distance is measured during the development or manufacture of the RFID tag. Conventionally, the communication limit distance is measured by, for example, gradually separating the RFID tag from the external device separated for a distance in which communication with the external device is possible to obtain a distance in which communication becomes impossible or by gradually approximating the RFID tag to the external device separated from the external device for a distance in which communication is impossible to thereby obtain a distance in which communication becomes possible (for example, see Japanese Laid-open Patent Publication No. 2006-322915). However, the RFID tag needs to be finely moved during the measurement in such a measurement method, which is significantly cumbersome, inhibiting efficiency of RFID tag development and manufacturing. 
     Thus, a technique is under consideration in which a correspondence between the distance from an external device that emits a radio signal with a predetermined output and the electric field strength of the radio signal as well as a correspondence between the size of the output by the external device and the electric field strength of the radio signal at a point separated from the external device for a predetermined distance are measured in advance, and the communication limit distance is measured by increasing and decreasing the size of the output by the external device without moving the RFID tag from a fixed position separated from the external device for a predetermined distance. To measure the communication limit distance, the size of the output by the external device is gradually decreased from the size in which the RFID tag can communicate to thereby obtain the size in which communication becomes impossible, or conversely, the size of the output by the external device is gradually increased from the size in which the RFID tag cannot communicate to thereby obtain the size in which communication becomes possible. The two kinds of correspondences measured in advance are used to convert the obtained size to the distance from the external device. The communication limit distance can be obtained through the series of processes without moving the RFID tag from the fixed position that is a predetermined distance apart from the external device. 
     However, the communication limit distance obtained without moving the RFID tag often does not match with the actual communication limit distance of the RFID tag in the technique. Therefore, the technique has a problem that the measurement accuracy of the communication limit distance is low. 
     Although the problem in the measurement of the communication limit distance has been described with the RFID tag as an example, such a problem is not limited to the RFID tag but may commonly occur in the measurement of the communication limit distance of an electronic device that receives and reacts to a radio signal. 
     SUMMARY 
     According to an aspect of the invention, a testing device includes a signal outputting section that has unique output characteristics and that outputs a predetermined electrical signal with electric power corresponding to a specified output level with the output characteristics when the output level is specified from multiple output levels; a specifying section that specifies the output level to the signal outputting section; a transmitting section that is supplied with the electrical signal outputted by the signal outputting section and that transmits a radio signal corresponding to the electrical signal to an electronic device that receives and reacts to the radio signal from a predetermined distance that is allowed to be a zero distance; a reaction checking section that checks the existence of the reaction in the electronic device; and a converting section that obtains an electric field strength of the radio signal received by the electronic device using the output characteristics of the signal outputting section from the output level specified by the specifying section and that converts the electric field strength to a distance between a predetermined antenna and the electronic device, the antenna transmitting the radio signal with a predetermined output and the electronic device receiving the radio signal in a same electric field strength as the electric field strength. 
     An object and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  depicts an RFID tag testing device as a first specific embodiment of a testing device; 
         FIG. 2  is a functional block diagram focusing on an internal configuration of a reader/writer  200  of the RFID tag testing device  1  of  FIG. 1 ; 
         FIG. 3  is a functional block diagram illustrating details of a control device  300  depicted in  FIG. 1 ; 
         FIG. 4  depicts an example of an electric field strength table; 
         FIG. 5  depicts an operation screen for measurement process of a communication limit distance; 
         FIG. 6  is a flow chart illustrating a flow of a process in the measurement process of the communication limit distance executed using the operation screen for measurement process  350 ; 
         FIG. 7  depicts an RFID tag testing device as a second specific embodiment of the testing device; 
         FIG. 8  is a functional block diagram illustrating details of a control device  500  depicted in  FIG. 7 ; 
         FIG. 9  depicts a first half of an example of the characteristic table; 
         FIG. 10  depicts a second half of the example of the characteristic table; 
         FIG. 11  is a graph of the content of the characteristic table depicted in  FIGS. 9 and 10 ; 
         FIG. 12  depicts an operation screen for measurement process of a communication limit distance in the control device  500  of  FIG. 8 ; 
         FIG. 13  is a graph of a relationship between the electric field strength and the distance depicted in  FIGS. 9 and 10 ; 
         FIG. 14  is a flow chart illustrating a flow of a process in the measurement process of the communication limit distance executed using the operation screen for measurement process  550 ; 
         FIG. 15  is a graph of a conversion relationship between the electric field strength and the distance using a default reference electric field strength “0 (dBm)”; and 
         FIG. 16  depicts how a deviation is eliminated in a distance reference mode. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Specific embodiments of the testing device and the testing method described in the present invention will now be described with reference to the drawings. 
     A first specific embodiment of the testing device will be described first. 
       FIG. 1  depicts an RFID tag testing device as the first specific embodiment of the testing device. 
     After receiving a command signal as a radio signal in compliance with a predetermined communication standard, the RFID tag testing device  1  illustrated in  FIG. 1  mounted with antenna patterns and IC chips for radio communication executes performance testing, such as measuring a communication limit distance described below, in relation to the communication performance of an RFID tag T 1  that returns a response to the command signal as a radio signal (response signal). The RFID tag T 1  handled by the RFID tag testing device  1  of the present embodiment is a so-called passive RFID tag that does not include an operational power supply and that is supplied with electric power for operation as a radio signal from outside. 
     The RFID tag testing device  1  includes a stripline cell  100 , a reader/writer  200 , and a control device  300 . The reader/writer  200  is connected to the control device  300  through a first cable  41 , and the stripline cell  100  is connected to the reader/writer  200  through a second cable  42 . The RFID tag T 1  is equivalent to an example of the electronic device of the testing device in the present invention, and the stripline cell  100  is equivalent to an example of the transmitting section as well as the stripline cell of the testing device in the present invention. The reader/writer  200  is equivalent to an example of the signal output section of the testing device in the present invention. 
     The communication limit distance of the RFID tag T 1  denotes a maximum distance among the distances that the RFID tag T 1  can respond in a situation in which a predetermined antenna used for the actual communication with the RFID tag T 1  is connected to the reader/writer  200 , the antenna transmits a radio signal with a predetermined output used for the actual communication, and the RFID tag T 1  receives the radio signal. In the situation, the electric field strength of the radio signal received by the RFID tag T 1  decreases as the RFID tag T 1  moves away from the antenna and increases as the RFID tag T 1  moves closer to the antenna. In the RFID tag testing device  1  of the present embodiment, the increase and decrease of the electric field strength is simulated by the increase and decrease of the output level of the reader/writer  200  as described below, and a minimum output level among the output levels that the RFID tag T 1  could respond is converted to a distance between the antenna and the RFID tag T 1  in the situation to thereby obtain the communication limit distance. 
     The stripline cell  100  includes a first conducting plate  101  with a width greater than the width of the RFID tag T 1  to be tested and a second conducting plate  102  opposing the first conducting plate  101 . One end of the first conducting plate  101  is connected to the second cable  42 , and the reader/writer  200  supplies the command signal to the first conducting plate  101  through the one end. The other end of the first conducting plate  101  is connected to a terminating resistance  103 . In the stripline cell  100 , when the reader/writer  200  supplies the command signal to the first conducting plate  101 , the command signal is transmitted to a predetermined propagation area A 1  as a radio signal of an output corresponding to the electric power of the command signal. The RFID tag  1  to be tested is arranged in the propagation area A 1  in the present embodiment. When the RFID tag T 1  receives the command signal and returns a response signal, the stripline cell  100  receives the response signal. The received response signal is transmitted to the reader/writer  200  through the second cable  42 . 
     The reader/writer  200  receives a command to the RFID tag T 1  from the control device  300  and generates a command signal based on the command through encoding and modulation according to a predetermined communication standard. The reader/writer  200  is specified with an output level to the stripline cell  100  by the control device  300 . 
     In the present embodiment, 63 output levels can be specified to the reader/writer  200  with 63 kinds of specified values from “0”, corresponding to the maximum level, to “62”, corresponding to the minimum level. When the control device  300  specifies an output level with one of the specified values, the reader/writer  200  generates a command signal with electric power corresponding to the specified output level. The reader/writer  200  includes unique output characteristics, and when an output level is specified, the reader/writer  200  generates a command signal with electric power corresponding to the specified output level with the output characteristics and supplies the command signal to the stripline cell  100 . The output characteristics of the reader/writer  200  do not change linearly from the maximum level to the minimum level. The output characteristics are nonlinear, the output characteristics being substantially constant at the maximum level near the specified value “0” and substantially constant at the minimum level near the specified value “62”. 
     The reader/writer  200  is selected from multiple reader/writers with different output characteristics and incorporated into the RFID tag testing device  1 . 
     After supplying the command signal, the reader/writer  200  supplies a signal for supplying power to the RFID tag T 1  to the stripline cell  100  as described below and continues to wait for a response signal from the RFID tag T 1  to be transmitted from the stripline cell  100  throughout a predetermined waiting time. If the response signal is transmitted from the stripline cell  100  within the waiting time, the reader/writer  200  modulates and decodes the response signal in accordance with the communication standard to generate a response for the control device  300  and transmits the response to the control device  300  after the waiting time. If the response signal is not transmitted within the waiting time, the reader/writer  200  generates a response indicating that the RFID tag T 1  does not respond to the command and transmits the response to the control device  300  after the waiting time. 
     The control device  300  transmits a command to the RFID tag T 1  to the reader/writer  200  and transmits a level specifying signal for specifying an output level with the specified value to the reader/writer  200 . The control device  300  further converts the output level (specified value) specified by the level specifying signal transmitted to the reader/writer  200  to a distance between a predetermined antenna and the RFID tag T 1 , the antenna used for the actual communication with the RFID tag T 1  being connected to the reader/writer  200 , and then displays the distance on a displaying device  300   a.    
     In the present embodiment, the control device  300  sequentially increases or sequentially decreases the output level by a predetermined operation by a user or by internal processing of the control device  300 . As described, the specified value “0” corresponds to the maximum output level and the specified value “62” corresponds to the minimum output level in the present embodiment. Therefore, an increase in the output level substantially denotes a decrease in the specified value, while a decrease in the output level substantially denotes an increase in the specified value. 
     The increase and decrease of the output level leads to an increase and decrease of the electric field strength of the command signal transmitted by the stripline cell  100  and received as a radio signal by the RFID tag T 1 . Meanwhile, in the condition in which the antenna is connected to the reader/writer  200 , the antenna transmits the command signal as a radio signal with a predetermined output used for the actual communication, and the RFID tag T 1  receives the command signal, moving close and away of the RFID tag T 1  with respect to the antenna also leads to an increase and decrease of the electric field strength of the command signal received by the RFID tag T 1 . In the present embodiment, the moving close and away of the RFID tag T 1  with respect to the antenna is simulated by sequentially increasing or sequentially decreasing the output levels of the reader/writer  200  and converting the output levels (specified values) to the distance, without using the antenna for the actual communication and without moving the RFID tag T 1 . 
     The control device  300  checks the existence of responses from the RFID tag T 1  in relation to the increase and decrease of the output levels and further calculates the distance corresponding to each output level and displays the distance on the displaying device  300   a.    
     The communication limit distance of the RFID tag T 1  is the maximum distance among the distances that the RFID tag T 1  could return the response signals in the situation described above. In the present embodiment, the moving close and away of the RFID tag T 1  with respect to the antenna is simulated by the increase and decrease in the output level of the reader/writer  200 . Therefore, the communication limit distance can be obtained as a conversion result from the minimum output level (maximum specified value) among the output levels that the RFID tag T 1  could return the response signals. The displaying device  300   a  displays the distance of the conversion result as a communication limit distance of the RFID tag T 1 . The process for acquiring the communication limit distance will be described in detail below. 
     The RFID tag testing device  1  is roughly constituted as described. 
     The reader/writer  200  will now be described in detail. 
       FIG. 2  is a functional block diagram focusing on an internal configuration of the reader/writer  200  of the RFID tag testing device  1  of  FIG. 1 . 
     The reader/writer  200  includes interface means  201 , command transmitting means  202 , transmission power level control means  203 , transmitting and receiving wave separating means  204 , and response receiving means  205 . 
     When receiving a command to the RFID tag T 1  from the control device  300 , the interface means  201  transmits the command to the command transmitting means  202 . When receiving a level specifying signal for specifying the output level of the reader/writer  200  with the specified value from the control device  300 , the interface means  201  transmits the level specifying signal to the transmission power level control means  203 . After transmitting the command to the command transmitting means  202 , the interface means  201  continues to wait for a response to the control device  300  in relation to the command throughout a predetermined waiting time. When the response is transmitted from the response receiving means  205  within the waiting time, the interface means  201  transmits the response to the control device  300 . If the response is not transmitted within the waiting time, the interface means  201  generates a response indicative of no response and transmits the response to the control device  300 . 
     When receiving a command from the interface means  201 , the command transmitting means  202  encodes the command in accordance with a communication protocol or a data format predefined by a predetermined communication standard to generate a timing signal and transmits the timing signal to the transmission power level control means  203 . 
     When receiving a level specifying signal from the interface means  201 , the transmission power level control means  203  generates a carrier signal of electric power according to the output level specified by the level specifying signal. When receiving the timing signal from the command transmitting means  202 , the transmission power level control means  203  uses the timing signal to modulate the carrier signal in accordance with a predetermined modulation method to thereby generate a command signal corresponding to the command from the control device  300 . The transmission power level control means  203  then transmits the generated command signal to the transmitting and receiving wave separating means  204 . After transmitting the command signal, the transmission power level control means  203  continues to transmit the carrier signal used to generate the command signal to the transmitting and receiving wave separating means  204  throughout the waiting time. 
     When receiving a command signal from the transmission power level control means  203 , the transmitting and receiving wave separating means  204  outputs the command signal to the stripline cell  100 . Following the command signal, the transmitting and receiving wave separating means  204  further outputs the carrier signals transmitted throughout the waiting time to the stripline cell  100 . When receiving a response signal from the RFID tag T 1  from the stripline cell  100 , the transmitting and receiving wave separating means  204  transmits the response signal to the response receiving means  205 . 
     When receiving a response signal from the transmitting and receiving wave separating means  204 , the response receiving means  205  demodulates and decodes the response signal in accordance with the communication standard to generate a response to the control device  300  and then transmits the response to the interface means  201 . 
     The control device  300  will now be described in detail. 
       FIG. 3  is a functional block diagram depicting details of the control device  300  illustrated in  FIG. 1 . 
     The control device  300  includes a text inputting section  301 , a trigger inputting section  302 , and an input receiving section  303 . Text information is inputted to the text inputting section  301  through a keyboard or the like. A trigger order such as an execution order of a predetermined process through a click operation of mouse or a depression operation of a predetermined key on the keyboard is inputted to the trigger inputting section  302 . The input receiving section  303  receives an input to the inputting sections. 
     The control device  300  also includes an internal timer  304  and an output level setting section  305 . The internal timer  304  informs the components in the control device  300  of every passage of predetermined time. The output level setting section  305  sets an output level of the reader/writer  200  to an output level/command constructing section  306  described below with the specified value. In the present embodiment, every time a user executes a predetermined operation and the execution is informed from the input receiving section  303 , or every time the passage of time is informed from the internal timer  304 , the output level setting section  305  increases or decreases the output level to be set to the output level/command constructing section  306  by “1” with the specified value. In this way, the moving close and away of the RFID tag T 1  with respect to the antenna in the situation described above is simulated. 
     The output level/command constructing section  306  generates a level specifying signal for specifying the output level set by the output level setting section  305  with the specified value and constructs a command to the RFID tag T 1 . The output level/command constructing section  306  further transmits the output level transmitted from the output level setting section  305  to a distance calculation processing section  312  described below. 
     The control device  300  further includes an output level/command transmitting section  307  and an R/W interface section  308 . The output level/command transmitting section  307  transmits a level specifying signal and a command to the reader/writer  200  through the R/W interface section  308 . The output level/command transmitting section  307  also transfers a command the same as the transmitted command to a response receiving section  309  described below. The R/W interface section  308  exchanges various signals with the reader/writer  200 . The command transmitted by the output level/command transmitting section  307  is transmitted to the reader/writer  200  through the R/W interface section  308 , and a response to the command is transmitted to the response receiving section  309  described below through the R/W interface section  308 . 
     The control device  300  includes the response receiving section  309  and a response analyzing section  310 . The response receiving section  309  receives the response to the command from the reader/writer  200  through the R/W interface section  308 . The response analyzing section  310 , for example, analyzes whether the response indicates existence or nonexistence of response from the RFID tag T 1 . As described, a command the same as the command transmitted by the output level/command transmitting section  307  is transferred to the response receiving section  309  from the output level/command transmitting section  307 . After receiving the response, the response receiving section  309  transfers a set of the received response and the command to the response analyzing section  310 . During the analysis of the transferred response, the response receiving section  309  also analyzes, for example, the existence of an occurrence of a communication error. The analysis result is transmitted to a display processing section  313  described below. 
     A combination of the output level setting section  305 , the output level/command constructing section  306 , the output level/command transmitting section  307 , and the R/W interface section  308  is equivalent to an example of the specifying section of the testing device in the present invention. A combination of the R/W interface section  308 , the response receiving section  309 , and the response analyzing section  310  is equivalent to an example of the reaction checking section in the present invention. 
     The control device  300  also includes an electric field strength storage section  311 . The electric field strength storage section  311  stores an electric field strength table describing one-to-one correspondence between specified values from “0” to “62” denoting the 63 output levels that can be specified to the reader/writer  200  and the electric field strength of the command signal transmitted by the stripline cell  100  as a radio signal when the output levels are specified to the reader/writer  200  with the specified values. The electric field strength storage section  311  is equivalent to an example of the storage section of the testing device in the present invention. 
       FIG. 4  depicts an example of the electric field strength table. 
     The electric field strength table Tb 1  illustrated in  FIG. 4  describes the one-to-one relationship between 63 specified values from “0” to “62” denoting the output levels and the electric field strength corresponding to the specified values and is equivalent to an example of the characteristic table of the testing device in the present invention. As described, the specified value “0” is equivalent to the maximum level and the specified value “62” is equivalent to the minimum level in the present embodiment. However, as described, the output characteristics of the reader/writer have nonlinear characteristics that are substantially constant at the maximum level near the specified value “0” and substantially constant at the minimum level near the specified value “62”. Consequently, in the electric field strength table Tb 1  illustrated in  FIG. 4 , the output characteristics are substantially constant at the maximum electric field strength “5.4 (dBm)” from about the specified value “0” to the specified value “6”. Subsequently, the electric field strength is decreased in accordance with an increase in the specified value, and the output characteristics are substantially constant at “−11.4 (dBm)” as the minimum electric field strength from about the specified value “40” to the specified value “62”. 
       FIG. 4  illustrates a conversion result adjacent to the electric field strength table Tb 1 , in which each electric field strength is converted to a distance between a predetermined antenna and the RFID tag T 1  when the antenna for the actual communication with the RFID tag T 1  is connected to the reader/writer  200 . The conversion to the distance will be described in detail below. 
     The correspondence described in the electric field strength table Tb 1  reflects the unique output characteristics included in the reader/writer  200 . In the present embodiment, the electric field strength storage section  311  stores electric field strength tables reflecting unique output characteristics of each of the multiple reader/writers from which the reader/writer  200  is selected when the RFID tag testing device  1  of  FIG. 1  is constructed. In the present embodiment, as illustrated in  FIG. 4 , the electric field strength is expressed in the electric field strength table with a unit “dBm” for simplification of the subsequent calculation. In the present embodiment, the electric field strength tables of the reader/writers are obtained from actual measurements. The measurements can be easily performed by incorporating the multiple reader/writers into the RFID tag testing device  1  of  FIG. 1  and measuring the electric field strength of the command signal transmitted by the stripline cell  100  with a standard dipole antenna for each of the 63 output levels. 
     In the control device  300  illustrated in  FIG. 3 , the user specifies the reader/writer  200  included in the RFID tag testing device  1  of  FIG. 1  among the multiple reader/writers whose electric field strength tables are stored in the electric field strength storage section  311  to measure the communication limit distance. Consequently, the input receiving section  303  transmits the specification result to the electric field strength storage section  311 , and the electric field strength storage section  311  selects an electric field strength table corresponding to the specified reader/writer  200  among the multiple electric field strength tables and transfers the electric field strength table to the distance calculation processing section  312  described below. 
     The distance calculation processing section  312  illustrated in  FIG. 3  converts the output level (specified value) set by the output level setting section  305  to the distance between the predetermined antenna connected to the reader/writer  200  and the RFID tag T 1 . The distance calculation processing section  312  is equivalent to an example of the converting section of the testing device in the present invention. The conversion from the output level to the distance by the distance calculation processing section  312  is performed by using the electric field strength table transferred from the electric field strength storage section  311  described in detail below. The distance calculation processing section  312  transfers the conversion result to the display processing section  313  described below. 
     The control device  300  includes a display processing section  313 , a text displaying section  314 , and a graphic displaying section  315 . The display processing section  313  generates a screen to be displayed on the displaying device  300   a  illustrated in  FIG. 1 . The text displaying section  314  displays text information among the constituent elements of the screen on the displaying device  300   a . The graphic displaying section  315  displays graphic information among the constituent elements of the screen. In the present embodiment, the distance as a conversion result, the analysis result in the response analyzing section  310 , and the like are displayed on the displaying device  300   a  as text information or graphic information. A combination of the display processing section  313 , the text displaying section  314 , and the graphic displaying section  315  is equivalent to an example of the conversion result displaying section of the testing device in the present invention. 
     In the measurement process of the communication limit distance of the RFID tag T 1  by the RFID tag testing device  1  of  FIG. 1 , as described, the output level setting section  305  sequentially increases or sequentially decreases the output level of the reader/writer  200  with the specified value every time the user performs a predetermined operation or every time there is a notification of the passage of time from the internal timer  304 . The response analyzing section  310  then checks the existence of a response from the RFID tag T 1  for each output level, and the distance calculation processing section  312  calculates the distance corresponding to each output level (specified value). 
     In the measurement process of the communication limit distance, the display processing section  313  displays, on the displaying device  300   a , the distance calculated by the distance calculation processing section  312  with respect to the minimum output level (maximum specified value) among the output levels in which the response analyzing section  310  has checked the existence of response as a communication limit distance of the RFID tag T 1  to be processed through the text displaying section  314  and the graphic displaying section  315 . In this way, the communication limit distance as the maximum distance among the distances in which the RFID tag T 1  to be processed could respond is displayed on the displaying device  300   a . The combination of the display processing section  313 , the text displaying section  314 , and the graphic displaying section  315  also serves as an example of the communication limit distance displaying section of the testing device in the present invention. 
     The measurement process of the communication limit distance of the RFID tag T 1  by the control device  300  is started when the user orders execution of the measurement process on an initial screen not illustrated and the following operation screen for measurement process is displayed on the displaying device  300   a  after the reception of the order. 
       FIG. 5  depicts the operation screen for measurement process of the communication limit distance. 
     In the present embodiment, as described, the output level setting section  305  sequentially increases or sequentially decreases the output level (specified value) of the reader/writer  200  to simulate the approach of the RFID tag T 1  to the antenna or the isolation from the antenna in the situation described above. 
     The operation screen for measurement process  350  illustrated in  FIG. 5  includes a measurement direction specifying section  351  for a user to specify whether to execute the measurement process of the communication limit distance by simulating isolation from the antenna or by simulating approach to the antenna. The measurement direction specifying section  351  includes an isolation direction specifying button  351   a  for specifying an isolation direction for isolating the RFID tag T 1  from the antenna and an approximation direction specifying button  351   b  for specifying an approximation direction for approximating the RFID tag T 1  to the antenna. 
     In the measurement process of the communication limit distance in the present embodiment, the sequential isolation or approximation to and from the predetermined antenna, i.e. the sequential increase or decrease of the output level (specified value) of the reader/writer  200 , is executed every time the user performs a predetermined operation or every time there is a notification from the internal timer  304  as described. Thus, two kinds of measurement methods are prepared in the present embodiment: a manual scan for executing the measurement process of the communication limit distance by sequentially receiving user&#39;s operations; and an auto scan for executing the measurement process by receiving notifications from the internal timer  304 . 
     The operation screen for measurement process  350  illustrated in  FIG. 5  includes a manual scanning section  352  operated by the user upon the manual scan and an auto scanning section  353  operated by the user upon the auto scan. The manual scanning section  352  includes a measurement button  352   a  sequentially operated by the user. In the manual scan, the output level is increased or decreased, the existence of response is checked, and the output level is converted to the distance every time the user operates the measurement button  352   a  in sequence. The auto scanning section  353  includes a start button  353   a  for the user to announce the start of a series of processes of sequentially increasing or decreasing the output level, checking the existence of responses in relation to the output levels, and converting the output levels to the distance. 
     In the present embodiment, the measured communication limit distance can be saved as a file describing the communication limit distance. Two saving methods are prepared in the present embodiment: automatic saving for saving with a predetermined file name; and manual saving for saving with a desired file name. 
     The operation screen for measurement process  350  illustrated in  FIG. 5  includes an automatic saving section  354  that saves the communication limit distance by automatic saving and a manual saving section  355  that saves the communication limit distance by manual saving. 
     The automatic saving section  354  includes an automatic save specifying button  354   a  for specifying automatic saving and a file name specifying section  354   b  provided with a radio button for selecting a file name from “UID/EPC.txt” and “Data.txt” upon automatic saving. In the present embodiment, when the automatic save specifying button  354   a  is clicked at the beginning of the measurement process of the communication limit distance, the communication limit distance obtained in the subsequent measurement process is automatically described and saved in a file with the file name selected in the file name specifying section  354   b . In the present embodiment, if the automatic save specifying button  354   a  is not clicked at the beginning of the measurement process of the communication limit distance, the communication limit distance is saved by manual saving. 
     The manual saving section  355  includes a file name displaying section  355   a  that displays a list of file names of currently saved files, a file name inputting section  355   b  for inputting a desired file name, a save button  355   c  for ordering to save with the inputted file name, a disclose button  355   d  for ordering to open the desired file and to display the communication limit distance described in the file, a delete button  355   e  for ordering to delete a desired file, and a reference button  355   f  for allowing to specify a file to be disclosed by a click operation of the disclose button  355   d  or to specify a file to be deleted by a click operation of the delete button  355   e.    
     The manual saving of the communication limit distance is performed by the user inputting a desired file name to the file name inputting section  355   b  at the final stage of the measurement process and further clicking the save button  355   c . The communication limit distance obtained by the measurement process is described and saved in the file with the desired file name. The user first clicks the reference button  355   f  to display the communication limit distance described in a desired file among currently stored files or to delete the file. As a result, the access to the file name displaying section  355   a  is permitted. In that condition, the user points the file name of the desired file among the file names displayed on the file name displaying section  355   a  with a cursor and clicks the disclose button  355   d  or the delete button  355   e  to display the communication limit distance described in the file or to delete the file. 
     The operation screen for measurement process  350  illustrated in  FIG. 5  further includes a reader/writer specifying section  356  for the user to specify the reader/writer  200  included in the RFID tag testing device  1  among the multiple reader/writers from which the reader/writer  200  is selected when the RFID tag testing device  1  of  FIG. 1  is constructed. 
     The reader/writer specifying section  356  includes an operating section  356   a  in which the user performs a specifying operation. The operating section  356   a  includes a menu button  356   a _ 1 . When the user clicks the menu button  356   a _ 1 , a pull-down menu describing a list of the names of the multiple reader/writers is displayed. As the user clicks the name of the reader/writer  200 , the reader/writer  200  is specified and the name is displayed. The reader/writer specifying section  356  further includes a strength displaying section  356   b  that numerically displays the electric field strength obtained using the electric field strength table of the reader/writer  200  specified by the operating section  356   a  during the measurement process of the communication limit distance. As described, the output level (specified value) of the reader/writer  200  is sequentially increased or decreased during the measurement process of the communication limit distance. The strength displaying section  356   b  displays the electric field strength obtained by using the electric field strength table for each of the sequentially changed output levels. 
     The operation screen for measurement process  350  illustrated in  FIG. 5  further includes a port opening section  356  that orders opening of a communication port for exchanging signals with the reader/writer  200  in the control device  300 . The port opening section  357  includes an open button  357   a  for the user to order opening of the communication port. The user can click the open button  357   a  to cause the RFID tag testing device  1  to start the measurement process of the communication limit distance. The user can also click the open button  357   a  during the measurement process to order to retry the measurement process. 
     The operation screen for measurement process  350  illustrated in  FIG. 5  includes a tag type inputting section  358  for inputting the type of the RFID tag to be processed. The tag type inputting section  358  includes an input field  358   a  for the user to input the type. 
     The operation screen for measurement process  350  illustrated in  FIG. 5  further includes a trimming specifying section  359  that specifies the execution of trimming for sequentially increasing or decreasing the output level (specified value) of the reader/writer  200  within a predetermined range. The trimming specifying section  359  includes a trimming specifying button  359   a  for specifying with a click operation. The maximum specified value and the minimum specified value in the trimming range are also set to specify the execution of trimming, which will be described below. In the present embodiment, if the trimming specifying button  359   a  is not clicked, the maximum specified value upon the increase and decrease of the output level is the specified value “62” corresponding to the minimum output level, and the minimum specified value is the specified value “0” corresponding to the maximum output level. 
     The operation screen for measurement process  350  illustrated in  FIG. 5  includes: a text display screen  361  that displays the communication limit distance obtained by the measurement process or various information related to the measurement process as text; and a graphic displaying section  362  that graphically displays the change in the electric field strength relative to the change in the output level (specified value) in which the electric field strength numerically displayed on the strength displaying section  356   b  in the reader/writer specifying section  356  is displayed longitudinally, and the output level (specified value) of the reader/writer  200  is displayed transversely. In the graphic displaying section  362 , a vertical line  362   a  displays an output level corresponding to the communication limit distance. 
     The operation screen for measurement process  350  illustrated in  FIG. 5  further includes an electric field strength bar  363  for displaying the electric field strength at the present moment with bar, an output level display bar  364  that displays the output level at the present moment with bar, and a distance displaying section  365  that numerically displays the distance converted from the output level. 
     The operation screen for measurement process  350  illustrated in  FIG. 5  further includes a first setting section  366  that sets the maximum specified value in the trimming range and a second setting section  367  that sets the minimum specified value. Once the increase or decrease of the output level is started, the first setting section  366  numerically displays the specified values at each point of the increase in the output level, and the second setting section  367  numerically displays the specified value at each point of the decrease in the output level. 
     When setting the maximum specified value and the minimum specified value in the trimming range, after the trimming specifying button  359   a  is clicked, the first setting section  366  or the second setting section  367  is clicked, and the display of the setting section is changed from “&lt;” or “&gt;” to the numerical display. In that condition, a specified value increase button  364   a  or a specified value decrease button  364   b  of the output level display bar  364  is clicked until the numerical display in the setting sections indicate desired values. In the present embodiment, the numerical display in the setting section is increased or decreased by “1” every time the specified value increase button  364   a  or the specified value decrease button  364   b  is clicked once. If the setting section is clicked again when the numerical display in the display section becomes the desired numerical display, the maximum specified value or the minimum specified value is fixed to the value displayed on the specifying section. The maximum set value and the minimum set value are set by performing such an operation to the setting sections. 
     A flow of a process in the measurement process of the communication limit distance executed using the operation screen for measurement process  350  will now be described. In the description below, the constituent elements illustrated in  FIGS. 3 and 5  may be referenced without reference numerals. 
       FIG. 6  is a flow chart illustrating a flow of a process of the measurement process of the communication limit distance executed using the operation screen for measurement process  350 . 
     The process illustrated by the flow chart of  FIG. 6  is equivalent to a first specific embodiment of the testing method. 
     As described, the process of  FIG. 6  is started when the user orders execution of the measurement process on the initial screen not illustrated and the displaying device  300   a  displays the following operation screen for measurement process in response to the order. After the start of the process, the user first clicks the open button  357   a  of the port opening section  357 , and the communication port for exchanging signals with the reader/writer  200  opens in the control device  300  (step S 101 ). Consequently, the control device  300  turns to a standby state for accepting the following various input operations, and in the meantime, the user uses the operation screen for measurement process  350  to perform various input operations (step S 102 ). 
     In the input operation of step S 102 , the user specifies the reader/writer  200  included in the RFID tag testing device  1  through the reader/writer specifying section  356 , inputs the type of the RFID tag to be processed through the tag type inputting section  358 , specifies the execution of trimming through the trimming specifying section  359 , sets the trimming range through the output level display bar  364  and the first and second setting sections  366  and  367  in association with the specification of the execution of trimming, specifies the execution of automatic saving through the automatic saving section  354 , and specifies the measurement direction through the measurement direction specifying section  351 . The specifications of the execution of trimming and the automatic saving are executed if the user desires. If the user does not desire to specify the execution of trimming and does not specify the execution of trimming, the output levels are increased or decreased throughout the entire range of the specified values from “0” to “62” as described. If the user does not desire the automatic saving and does not specify the automatic saving, the saving process is executed as described with the desired file name through the manual saving section  355  at the end of the measurement process. 
     When the reader/writer  200  is specified in the input operation of step S 102 , the electric field strength storage section  311  selects an electric field strength table corresponding to the specified reader/writer  200  from the stored electric field strength tables and transfers the electric field strength table to the distance calculation processing section  312 . 
     After the input operation of step S 102 , the control device  300  turns to the standby state until the user clicks the measurement button  352   a  of the manual scanning section  352  or clicks the start button  353   a  of the auto scanning section  353  (step S 103 ). After the user performs these operations (Yes judgment in step S 103 ), the process advances to the next process (step S 104 ). 
     In step S 104 , the output level setting section  305  first sets the specified value at the start as the output level to the output level/command constructing section  306 . The specified value at the start is determined as follows depending on whether the execution of trimming is specified in step S 102  and which of the measuring directions is specified in step S 102 : the isolation direction for isolating the RFID tag from the predetermined antenna; or the approximation direction for approximating the RFID tag T 1  to the antenna, i.e. which of the decrease and the increase of the output level is specified. 
     If the execution of trimming is specified, the minimum specified value set in the second setting section  367  serves as the specified value at the start when the isolation direction is specified as the measurement direction, and the maximum specified value set in the first setting section  366  serves as the specified value at the start when the approximation direction is specified as the measurement direction. 
     On the other hand, if the execution of trimming is not specified, “0” serves as the specified value at the start when the isolation direction is specified as the measurement direction, and “62” serves as the specified value at the start when the approximation direction is specified as the measurement direction. 
     Once the specified value at the start is determined, the output level/command constructing section  306  generates a level specifying signal for specifying the output level with the specified value at the start and constructs a command to the RFID tag T 1  in the process of step S 104 . The output level/command transmitting section  307  transmits the level specifying signal and the command to the reader/writer  200 . The output level/command constructing section  306  also transfers the specified value at the start set by the output level setting section  305  to the distance calculation processing section  312  in step S 104 . The process of step S 104  is equivalent to an example of the specifying step of the testing method in the present invention. 
     As described, the reader/writer  200  turns to the standby state after supplying the command signal transmitted from the control device  300  to the stripline cell  100  and returns a response indicative of response or no response to the control device  300  after the waiting time. Meanwhile, the control device  300  executes the processes of steps S 105  and S 106  when the reader/writer  200  is in the standby state. 
     In step S 105 , the distance calculation processing section  312  first converts the specified value at the start set by the output level setting section  305  to the distance between the predetermined antenna used for the actual communication with the RFID tag T 1  and the RFID tag T 1 , the antenna being connected to the reader/writer  200  (step S 105 ). The process of step S 105  is equivalent to an example of the converting step of the testing method in the present invention. 
     As described, the electric field strength storage section  311  transfers the electric field strength table corresponding to the reader/writer  200  specified in the process of step S 102  to the distance calculation processing section  312 . The output level/command constructing section  306  transfers the specified value at the start indicated by the level specifying signal transmitted to the reader/writer  200  in the process of step S 104  to the distance calculation processing section  312 . 
     In the process of step S 105 , the electric field strength corresponding to the specified value at the start in the transferred electric field strength table is first obtained. 
     The obtained electric field strength is then converted to the distance between the antenna and the RFID tag T 1 . The conversion is performed using the following conversion formula based on the correspondence between the propagation distance of radio wave and the electric field strength, the conversion formula expressing a distance “D (cm)” from the antenna as a function of an electric field strength “P (dBm)” at a point separated by the distance “D (cm)”. 
     
       
         
           
             
               
                 
                   
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                           d 
                           
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                       100 
                     
                   
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                       1.01157945425989 
                     
                   
                 
               
               
                 
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     Formula (1) is a formula in which the electric field strength at the point separated by “100 (cm)” from the antenna is set to “0.6 (dBm)”, and “d” is a coefficient expressing the change in the distance when the electric field strength is changed for “0.1 (dBm)”. The electric field strength “0.6 (dBm)” at the point separated by “100 (cm)” from the antenna is a value obtained by measuring the electric field strength at the point separated by “100 (cm)” from the antenna in an anechoic chamber with the antenna being actually connected to the reader/writer  200 . 
     In step S 106 , the electric field strength obtained from the specified value at the start in the process of step S 105  is numerically displayed on the strength displaying section  356   b  of the reader/writer specifying section  356  and plotted on the graphic displaying section  362 . The distance between the antenna and the RFID tag T 1  converted from the specified value at the start is numerically displayed on the distance displaying section  365 . 
     When the reader/writer  200  transmits the response after the waiting time after the process of steps S 105  and S 106  are finished, the response analyzing section  310  analyzes the response to determine, for example, the existence of the response from the RFID tag T 1  and transmits the analysis result to the display processing section  313  (step S 107 ). The process of step S 107  is equivalent to an example of the reaction checking step of the testing method in the present invention. 
     The display processing section  313  receives the analysis result (step S 108 ). If the analysis result indicates the existence of response (Yes judgment in step S 108 ), the display processing section  313  displays the existence of response on the text display screen  361  (step S 109 ). If the analysis result indicates no response (No judgment in step S 108 ), the display processing section  313  displays the no response on the text display screen  361  (step S 110 ). 
     As described below, the process from step S 104  to step S 112  are repeated in the process illustrated in the flow chart of  FIG. 6 . In step S 109 , the display processing section  313  compares the current analysis result of step S 107  and the previous analysis result of step S 107 . If the results are different, the display processing section  313  numerically displays the current distance calculated in step S 105  as the communication limit distance of the RFID tag T 1  to be processed on the text display screen  361 , and the graphic displaying section  362  displays the output level (specified value) corresponding to the communication limit distance with the vertical line  362   a . In step S 110 , the display processing section  313  performs a similar comparison as in step S 109 . If the analysis results are different, the display processing section  313  numerically displays the previous distance calculated in step S 105  as the communication limit distance, and the output level (specified value) corresponding to the communication limit distance is displayed with the vertical line  362   a . Thus, in step S 109 , the distance calculated when the analysis result of the existence of response is obtained for the first time in step S 107  is displayed as the communication limit distance. In step S 10 , the distance calculated when the analysis result of the existence of response is obtained for the last time in step S 107  is displayed as the communication limit distance. 
     The control device  300  turns to the standby state when the display process of step S 109  or step S 110  is finished (step S 111 ). 
     The standby state of step S 111  continues until the user clicks the measurement button  352   a  again if the standby state of step S 103  has been removed by user&#39;s click operation of the measurement button  352   a  of the manual scanning section  352  (Yes judgment in step S 111 ). The standby state of step S 111  continues until the internal timer  304  informs a lapse of predetermined time if the standby state of step S 103  has been removed by a click operation of the start button  353   a  of the auto scanning section  353  (Yes judgment in step S 111 ). 
     If the standby state is removed after the second click operation of the measurement button  352   a  or the notification from the internal timer  304 , the output level setting section  305  increases or decreases the output level (specified value) by “1”, and the process returns to step S 104  (step S 112 ). In step S 112 , if the measurement direction specified in the process of step S 102  is the isolation direction, i.e. the direction in which the output level is decreased, the specified value is increased by “1”. If the specified measurement direction is the approximation direction, i.e. direction in which the output level is increased, the specified value is decreased by “1”. 
     In the process illustrated by the flow chart of  FIG. 6 , the process from step S 104  to step S 112  is repeated until a termination condition in step S 113  described below is met. 
     As described, in step S 109 , the distance calculated when the analysis result of the existence of response is obtained for the first time in step S 107  is displayed as the communication limit distance. In step S 110 , the distance calculated when the analysis result of the existence of response is obtained for the last time in step S 107  is displayed as the communication limit distance. In step S 112 , the output level (specified value) is increased by “1” or decreased by “1” during every repetition described above. Thus, the communication limit distance displayed in step S 109  or step S 110  is the distance converted from the minimum output level (maximum specified value) among the output levels (specified values) in which the analysis result of the existence of response are obtained in step S 107  and is the maximum distance that the RFID tag T 1  to be processed can return the response. 
     In step S 113 , if the measurement direction specified in the process of step S 102  is the approximation direction, i.e. the direction in which the output level is increased, and the execution of trimming is specified in step S 102 , the termination condition is determined to be met when the specified value that is increased or decreased by “1” in step S 112  reaches the specified value set in the second setting section  367 . If the measurement direction is the direction in which the output level is increased and the execution of trimming is not specified, the termination condition is determined to be met when the specified value reaches “0”. 
     If the specified measurement direction is the isolation direction, i.e. the direction in which the output level is decreased, and the execution of trimming is specified, the termination condition is determined to be met when the specified value reaches the specified value specified in the first setting section  366 . If the measurement direction is the direction in which the output level is decreased and the execution of trimming is not specified, the termination condition is determined to be met when the specified value reaches “62”. 
     If the termination condition is determined to be met in step S 113  (Yes judgment in step S 113 ), the communication limit distance displayed in step S 109  or step S 110  is saved (step S 114 ). 
     If the automatic saving is specified in step S 102 , the saving in step S 114  is automatically performed by describing the communication limit distance in the file attached with the file name specified by the selection with the radio button in the file name specifying section  354   b.    
     On the other hand, if the automatic saving is not specified in step S 102 , the text display screen  361  displays a message for inputting a file name to the file name inputting section  355   b  and for instructing saving with a click operation of the save button  355   c . When the user inputs a desired file name in the file name inputting section  355   b  and clicks the save button  355   c , the communication limit distance is described in a file with the desired file name to save the communication limit distance. 
     After the communication limit distance is displayed and saved in the process of step S 114 , the process illustrated in the flow chart of  FIG. 6  is terminated. 
     In the present embodiment, as described, if the user clicks the open button  357   a  of the port opening section  357  during the process from step S 102  to step S 114 , the execution up to then is reset, and the process is restarted from step S 102 . 
     In this way, the transmission of the command signal to the RFID tag T 1  and the checking of the response are repeated based on the user&#39;s order while increasing or decreasing the output level by “1” with the specified value in the present embodiment. This is equivalent to the gradual approximation or gradual isolation of the RFID tag T 1  to and from the antenna, which transmits the command signal with the predetermined output, from a sufficiently separated point, while checking the response of the RFID tag T 1 . The distance converted from the minimum output level (maximum specified value) serves as the communication limit distance of the RFID tag T 1 . 
     Therefore, according to the RFID tag testing device  1  of the present embodiment, the communication limit distance can be easily obtained by the manual scan with the user repeating the user&#39;s orders of step S 111  while checking the existence of the distance and the response displayed on the display screen  300   a  without moving the RFID tag T 1 . In the case of the auto scan, the communication limit distance can be easily obtained even without executing such orders. 
     In the present embodiment, as described in the process of step S 104 , the output level (specified value) is converted to the distance using the electric field strength table reflecting the output characteristics of the reader/writer  200  included in the RFID tag testing device  1 . Therefore, significantly accurate conversion to the distance is performed in the RFID tag testing device  1 , reflecting the actual output characteristics of the reader/writer  200 . As a result, the communication limit distance of the RFID tag T 1  can be obtained with high accuracy. The RFID tag testing device  1  stores such electric field strength tables of multiple reader/writers other than the reader/writer  200  included in the RFID tag testing device  1 . Therefore, even if another reader/writer replaces the reader/writer  200  included in the RFID tag testing device  1 , the communication limit distance can be obtained with high accuracy by specifying the reader/writer after the replacement. 
     In the present embodiment, the electric field strength of the command signal transmitted by the stripline cell  100  is obtained using the electric field strength table based on the output level (specified value) specified by the control device  300  to the reader/writer  200 , and the electric field strength is converted to the distance using the formula. 
     The electric field strength may be converted to the distance without using the formula as in the present embodiment by obtaining, in advance by the actual measurement, the relationship between the distance from the antenna that transmits the command signal with a predetermined output and the electric field strength and using the measurement result. In the method, the relationship between the distance from the antenna and the electric field strength is measured by, for example, measuring the electric field strength while gradually separating the electric field strength meter from the antenna in an anechoic chamber or the like. In this case, the conversion to a distance longer that the distance in which the electric field strength is measured in advance cannot be performed in the conversion using the relationship in which the distance and the electric field strength are measured. Therefore, the distance that can be converted is limited to the dimension of the place where the measurement is performed such as the dimension of the anechoic chamber. As a result, the communication limit distance cannot be obtained if the communication limit distance included in the RFID tag to be tested exceeds the upper limit of the distance that can be converted. 
     However, there is no upper limit to the distance that can be converted in the RFID tag testing device  1  of the present embodiment because the electric field strength is converted to the distance using the formula. Therefore, even a significantly long communication limit distance can be obtained. 
     The stripline cell  100  is used to transmit the command signal as a radio signal in the RFID tag testing device  1  of the present embodiment. As described, the stripline cell  100  transmits the radio signal in a condition where the propagation range is significantly limited. Therefore, the present embodiment enables to transmit the command signal to the RFID tag T 1  without using large-scale equipment such as an anechoic chamber and without electromagnetically affecting the ambient environment. 
     In this way, according to the RFID tag testing device  1  of the present embodiment, the communication limit distance of the RFID tag to be tested can be easily obtained with high accuracy. 
     A second specific embodiment of the testing device will now be described. 
     In the second embodiment, only a control device is different from the RFID tag testing device  1  of the first embodiment illustrated in  FIG. 1 . The second embodiment will now be described focusing on the difference. 
       FIG. 7  depicts an RFID tag testing device as the second specific embodiment of the testing device. 
     In  FIG. 7 , constituent elements equivalent to the constituent elements of  FIG. 1  are designated with the same reference numerals as in  FIG. 1 , and the repeated description will be omitted. 
     In relation to the multiple reader/writers, a control device  500  of an RFID tag testing device  2  illustrated in  FIG. 7  stores, in place of the electric field strength tables, characteristic tables denoting one-to-one correspondences between multiple output levels (specified values) specified to the reader/writers and electric power of the reader/writers corresponding to each output level (specified value). 
     In the present embodiment, the control device  500  receives inputs of a loss factor in the second cable  42  and a damping factor in the stripline cell  100  from the user. The control device  500  obtains the electric field strength using the characteristic table corresponding to the reader/writer  200  as well as the loss factor in the second cable  42  and the damping factor in the stripline cell  100  to obtain the electric field strength of the command signal transmitted by the stripline cell  100  from the output level (specified value) specified to the reader/writer  200 . A method for obtaining the electric field strength will be described in detail below. 
     In the present embodiment, the conversion formula for converting the electric field strength obtained as described above to the distance between the predetermined antenna, which is used for the actual communication with the RFID tag T 1 , and the RFID tag T 1  can be modified, the antenna being connected to the reader/writer  200 , the antenna transmitting the radio signal with the predetermined output used for the actual communication, and the RFID tag T 1  receiving the radio signal. The modification is made using a reference electric field strength or a reference distance described below, and the user inputs the reference electric field strength and the reference distance to the control device  500  in the present embodiment. The modification of the conversion formula will also be described in detail below. 
       FIG. 8  is a functional block diagram illustrating the details of the control device  500  depicted in  FIG. 7 . 
     In  FIG. 8 , constituent elements equivalent to the constituent elements of the control device  100  of the first embodiment illustrated in  FIG. 3  are designated with the same reference numerals as in  FIG. 3 , and the repeated description of the constituent elements will be omitted. 
     The control device  500  of the present embodiment includes: an output characteristic storage section  501  that stores the characteristic tables of the multiple reader/writers; a loss factor storage section  502  that stores the loss factor in the second cable  42  of  FIG. 7  inputted by the user; a damping factor storage section  503  that stores the damping factor in the stripline cell  100  of  FIG. 7  inputted by the user; a reference electric field/distance storage section  504  that stores the reference electric field and the reference distance described below inputted by the user; and a distance calculation processing section  505  that uses the characteristic tables, the loss factor, and the damping factor, modifies the conversion formula when the user inputs the reference electric field or the reference distance, uses the modified conversion formula to thereby perform the conversion to the distance. 
     A combination of the input receiving section  303  and the reference electric field/distance storage section  504  is equivalent to an example serving as the reference electric field strength inputting section and the reference distance inputting section of the testing device in the present invention. The distance calculation processing section  505  is equivalent to an example of the converting section of the testing device in the present invention. 
     The characteristic table will now be described. 
       FIG. 9  depicts a first half of an example of the characteristic table.  FIG. 10  depicts a second half of the example of the characteristic table.  FIG. 11  is a graph of the content of the characteristic table illustrated in  FIGS. 9 and 10 . 
     A characteristic table Tb 2   a  illustrated in  FIG. 9  describes a one-to-one correspondence between the 31 specified values from “0” to “30” denoting the output levels and electric power of the reader/writers  200  corresponding to the specified values. A characteristic table Tb 2   b  describes a one-to-one correspondence between 32 specified values from “31” to “62” and electric power. The characteristic table of a reader/writer is divided into  FIGS. 9 and 10  for convenient illustration. However, the output characteristic storage section  501  of  FIG. 8  stores a characteristic table describing the one-to-one correspondence between 63 specified values from “0” to “62” and electric power of a reader/writer. 
     The characteristic tables Tb 2   a  and Tb 2   b  illustrated in  FIGS. 9 and 10  indicate measurement values obtained by measuring the electric power actually outputted by the reader/writer  200  according to the specified values and expected values denoting the electric power theoretically predicted from the configuration of the reader/writer  200 . However, the expected values are illustrated for comparison, and the characteristic table stored in the output characteristic storage section  501  of  FIG. 8  only describes the specified values and the measurement values of the electric power. 
     A graph G 1  illustrated in  FIG. 11  depicts the content of the characteristic tables Tb 2   a  and Tb 2   b  illustrated in  FIGS. 9 and 10 . Sixty three specified values from “0” to “62” are displayed transversely. The electric power of the reader/writer  200  is displayed longitudinally. The graph G 1  of  FIG. 11  depicts the correspondence between 63 specified values and the expected values with a line L 1  connecting the black square marks and the correspondence between 63 specified values and the measurement values with a line L 2  connecting the white diamond marks. 
     As in the first embodiment, the specified value “0” corresponds to the maximum level in the output level, and the specified value “62” corresponds to the minimum level in the characteristic tables Tb 2   a  and Tb 2   b  of the present embodiment illustrated in  FIGS. 9 and 10 . The actual output characteristics of the reader/writer  200  do not linearly change from the maximum level to the minimum level as depicted by the line L 1  in the graph G 1  of  FIG. 11 , but are nonlinear as in the first embodiment. As depicted by the line L 2 , the output characteristics are nonlinear, the output characteristics being substantially constant at a maximum level “25.4 (dBm)” from about specified value “0” to specified value “6”, the output power decreasing as the specified value increases, and the output characteristics being substantially constant at a minimum level “8.0 (dBm)” from about specified value “40” to specified value “62”. 
     The output characteristic storage section  501  of  FIG. 8  stores characteristic tables of multiple reader/writers with different output characteristics. 
       FIGS. 9 and 10  depict three different cases of the total loss from the reader/writer  200  to the RFID tag T 1  in relation to the electric field strength of the radio signal transmitted by the stripline cell  100  when the output levels are specified to the reader/writer  200  with the specified values (cases where the total loss is 15 (dB), 20 (dB), and 10 (dB)). 
     The total loss is a loss on the path from the reader/writer to the RFID tag T 1  such as a sum of the loss factor in the second cable  42  and the damping factor of the stripline cell  100  in the RFID tag testing device  2  of  FIG. 7 . In the present embodiment, the second cable  42  in the RFID tag testing device  2  can be replaced by another cable with a different loss factor, or the stripline cell  100  can be replaced by another stripline cell with a different loss factor. Three total losses in  FIGS. 9 and 10  denote losses in three cases in which the cable or the stripline cell from the reader/writer  200  to the RFID tag T 1  is different. 
     As described, the user provides the loss factor in the cable and the damping factor in the stripline cell in the present embodiment, and the total loss is obtained as the sum of the loss factor and the damping factor. In the present embodiment, the loss factor and the damping factor are provided with a unit “dB”. In this way, the electric field strength, which is expressed by a unit “dBm” of the radio signal transmitted by the stripline cell when the output levels are specified to the reader/writer  200  with the specified values, can be obtained by subtracting the total value of the loss factor and the damping factor that is provided with a unit “dB” from the electric power expressed by a unit “dBm” corresponding to the specified values in the characteristic table. 
     Among the electric field strengths indicating three cases in  FIGS. 9 and 8 , the electric field strengths in the case where the total loss is 20 (dB) and in the case where the total loss is 10 (dB) are calculated as described. For example, if the total loss is 20 (dB), the electric field strength of the radio signal transmitted by the stripline cell when the output level is specified to the reader/writer  200  with the specified value “011 is “5.4 (dBm)” in which the total loss “20 (dB)” is subtracted from the electric power (measurement value) “25.4 (dBm)” corresponding to the specified value “0”. 
     In  FIGS. 9 and 8 , to compare with the two cases, the expected values of the electric field strength obtained by subtracting the total loss “15 (dB)” from the expected values of the electric power is illustrated as the electric field strength of the case where the total loss is 15 (dB). 
     In  FIGS. 9 and 10 , the distances converted from the electric field strength are illustrated for each of the three cases, and the conversion will be described below. 
     An operation screen for measurement process of the communication limit distance in the control device  500  of the present embodiment will now be described. 
       FIG. 12  depicts the operation screen for measurement process of the communication limit distance in the control device  500  of  FIG. 8 . 
     In  FIG. 12 , constituent elements equivalent to the constituent elements of the operation screen for measurement process  350  of the first embodiment illustrated in  FIG. 5  are designated with the same reference numerals as in  FIG. 5 . The repeated description of the constituent elements will be omitted. 
     As described, in the present embodiment, the characteristic table of the reader/writer  200  of  FIG. 7 , the loss factor in the second cable  42 , and the damping factor of the stripline cell  100  are used to obtain the electric field strength from the output level (specified value). As in the first embodiment, the characteristic table is obtained by the user specifying the reader/writer  200  of  FIG. 7 . Meanwhile, as described, the user numerically inputs the loss factor in the second cable  42  and the damping factor in the stripline cell  100 . The operation screen for measurement process  550  of  FIG. 12  includes a parameter setting section  551  in which the loss factor and the damping factor are inputted as parameters. 
     The parameter setting section  551  includes a loss factor inputting section  551   a  that is numerically inputted with the loss factor in the second cable  42  and a damping factor inputting section  551   b  that is numerically inputted with the damping factor in the stripline cell  100 . The inputs to the two inputting sections  551   a  and  551   b  are basically performed with numerical inputs through a keyboard not illustrated. In the present embodiment, the loss factor and the damping factor numerically inputted to the inputting sections  551   a  and  551   b  are stored in the loss factor storage section  502  and the damping factor storage section  503  of  FIG. 8  respectively. The loss factor and the damping factor can be easily inputted again by an operation of menu buttons  551   a _ 1  and  551   b _ 1  included in the inputting sections  551   a  and  551   b . When the menu button  551   a _ 1  or  551   b _ 1  is clicked, a list of the loss factors stored in the loss factor storage section  502  or a list of the damping factors stored in the damping factor storage section  503  are displayed, and the user points a desired loss factor or damping factor in the lists with the cursor to input the loss factor or the damping factor. 
     The parameter setting section  551  further includes an operating section  356   a  for specifying the reader/writer  200  and a strength displaying section  356   b  that numerically displays the electric field strength during the measurement process of the communication limit distance, similar to the operating section  356   a  and the strength displaying section  356   b  included in the reader/writer specifying section  356  of the operation screen for measurement process  350  of the first embodiment. 
     In the present embodiment, the following formula is used as a conversion formula for converting the electric field strength to the distance between the predetermined antenna and the RFID tag T 1  in the situation described above. 
     
       
         
           
             
               
                 
                   
                     D 
                     = 
                     
                       
                         { 
                         
                           d 
                           
                             ( 
                             
                               
                                 Pr 
                                 - 
                                 P 
                               
                               0.1 
                             
                             ) 
                           
                         
                         } 
                       
                       × 
                       Dr 
                     
                   
                    
                   
                     
 
                   
                    
                   
                     d 
                     = 
                     
                       
                         10 
                         
                           ( 
                           
                             0.1 
                             20 
                           
                           ) 
                         
                       
                       ≈ 
                       1.01157945425989 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
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                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     In Formula 2, “D (cm)” denotes a distance between the predetermined antenna and the RFID tag T 1 , “d” denotes a coefficient expressing a change in the distance when the electric field strength is changed by “0.1 (dBm)”, “P (dBm)” denotes an electric field strength, “Pr (dBm)” denotes a reference electric field strength described below, and “Dr (cm)” denotes a reference distance described below. 
     The reference electric field strength denotes an electric field strength that needs to be converted to the reference distance by Formula 2. In the present embodiment, although the reference electric field strength “0 (dBm)” is provided by default, the user can properly modify the reference electric field strength. The reference distance denotes a distance with which the reference electric field strength needs to be converted by Formula 2. In the present embodiment, although the reference distance “100 (cm)” is provided by default, the user can properly modify the reference distance. The conversion relationship expressed by the conversion formula 2, where the reference electric field strength “Pr (dBm)” is “0 (dBm)” and the reference distance “Dr (cm)” is “100 (cm)”, is equivalent to an example of the initial relationship of the testing device in the present invention. The conversion relationship expressed by the conversion formula (2), where at least one of the reference electric field strength “Pr (dBm)” and the reference distance “Dr (cm)” is a modified value from the user, is equivalent to an example of the modified relationship of the testing device in the present invention. 
     The distance in three cases with different total losses described in  FIGS. 9 and 10  is obtained by a conversion by Formula 2, where the reference electric field strength “Pr (dBm)” is a modified value “0.6 (dBm)” from the user, and the reference distance “Dr (cm)” is a default reference distance “100 (cm)”. 
       FIG. 13  is a graph of the relationship between the electric field strength and the distance illustrated in  FIGS. 9 and 10 . 
     In a graph G 2  illustrated in  FIG. 13 , the distance is displayed transversely, and the electric field strength is displayed longitudinally. The graph G 2  describes Formula 2 with a line L 3 , where the reference electric field strength “Pr (dBm)” is “0.6 (dBm)” and the reference distance “Dr (cm)” is “100 (cm)”. On the line  3 , white triangle marks plot the relationship between the expected value of the electric field strength and the distance when the total loss is 15 (dB). White circle marks plot the relationship between the electric field strength and the distance when the total loss is 20 (dB). White square marks plot the relationship between the electric field strength and the distance when the total loss is 10 (dB). 
     As can be seen from the line L 3 , Formula 2 expresses the relationship in which the electric field strength decreases by 6 (dB) if the distance is doubled, i.e. the size becomes one-fourth. Formula 2 is based on physical laws in the relationship between the electric field strength of the radio wave that emits a predetermined radio source and that propagates in the free space and the distance from the radio source. 
     In the present embodiment, the control device  500  includes two modes described below, an electric field reference mode and a distance reference mode, as operation modes for conversion using Formula 2. 
     The electric field reference mode is a mode in which the reference distance “Dr (cm)” is fixed to a default “100 (cm)”, and a default “0 (dBm)” or a modified value from the user is used as the reference electric field strength “Pr (dBm)” to perform the conversion. Meanwhile, the distance reference mode is a mode in which modified values from the user are used for both of the reference electric field strength “Pr (dBm)” and the reference distance “Dr (cm)” to perform the conversion. The modified values in the two modes will be described in detail below. 
     The operation screen for measurement process  550  of  FIG. 12  includes: an electric field reference mode setting section  552  for performing an execution order of the electric field reference mode, a modification request of the reference electric field strength “Pr (dBm)”, and an input of the reference electric field strength “Pr (dBm)”; and a distance reference mode setting section  553  for performing an execution order of the distance reference mode, a modification request of the reference distance “Dr (cm)”, and an input of the reference distance “Dr (cm)”. 
     The electric field reference mode setting section  552  includes: an electric field reference mode request button  552   a  for ordering execution of the electric field reference mode and requesting modification of the reference electric field strength “Pr (dBm)”; and a reference electric field strength inputting section for electric field reference mode  552   b  for inputting the reference electric field strength “Pr (dBm)” for the electric field reference mode. An input to the reference electric field strength inputting section for electric field reference mode  552   b  is permitted by clicking the electric field reference mode request button  552   a.    
     The distance reference mode setting section  553  includes: a distance reference mode request button  553   a  for ordering execution of the distance reference mode and requesting modification of the reference distance “Dr (cm)”; a reference distance inputting section  553   b  for inputting the reference distance “Dr (cm)”; and a reference electric field strength inputting section for distance reference mode  553   c  for inputting the reference electric field strength “Pr (dBm)” for the distance reference mode. An input to the reference distance inputting section  553   b  and the reference electric field strength inputting section for distance reference mode  553   c  is permitted by clicking the distance reference mode request button  553   a.    
     The operation screen for measurement process  550  of  FIG. 12  includes a distance displaying section  554  that displays the distance converted from the output level at the present moment displayed with bar on the output level display bar  364  as well as the operation mode at the present moment. In the present embodiment, the reference electric field strength “Pr (dBm)” can be modified, or the operation mode can be changed to the distance reference mode during the measurement process of the communication limit distance in the electric field reference mode. If the reference electric field strength “Pr (dBm)” is modified, or if the operation mode is changed to the distance reference mode, there is a high possibility that the converted distance has a different value from the distance converted under the conditions at the beginning of the measurement process. The distance displaying section  554  displays the distance converted under the conditions at the beginning in parenthesis. In an example of  FIG. 12 , the operation mode is the electric field reference mode, and the reference electric field strength “Pr (dBm)” is not modified during the process. Therefore, the distance converted from the output level at the present moment and the distance displayed in parenthesis correspond. 
     A flow of the process in the measurement process of the communication limit distance executed using the operation screen for measurement process  550  described above will now be described. In the following description, the constituent elements illustrated in  FIGS. 8 and 10  may be referenced without reference numerals. 
       FIG. 14  is a flow chart illustrating a flow of the process in the measurement process of the communication limit distance executed using the operation screen for measurement process  550 . 
     The process illustrated in the flow chart of  FIG. 14  is equivalent to a second specific embodiment of the testing method. 
     In  FIG. 14 , processes equivalent to the processes in the flow chart of  FIG. 6  are designated with the same reference numerals as in  FIG. 6 , and the repeated description will be omitted. 
     When the process illustrated by the flow chart of  FIG. 14  is started, and the user clicks the open button  357   a  of the port opening section  357  to open the communication port in the control device  500  (step S 101 ), the control device  500  turns to the standby state for receiving the following various input operations (step S 201 ). 
     In the input operations of step S 202 , the reader/writer  200  included in the RFID tag testing device  2  is specified, the loss factor in the second cable  42  is inputted, the damping factor in the stripline cell  100  is inputted, the operation mode is specified, the reference electric field strength “Pr (dBm)” is inputted, the reference distance “Dr (cm)” is inputted, the type of the RFID tag to be applied is inputted, the execution of trimming is specified, the trimming range associated with the specification is set, the execution of automatic saving is specified, and the measurement direction is specified. 
     The execution of trimming and automatic saving are specified if the user desires. In addition, the reference electric field strength “Pr (dBm)” and the reference distance “Dr (cm)” are inputted if the user desires. 
     The user clicks one of the electric field reference mode request button  552   a  and the distance reference mode request button  553   a  to specify the operation mode. The electric field reference mode is specified as the operation mode if the electric field reference mode request button  552   a  is clicked. The distance reference mode is specified as the operation mode if the distance reference mode request button  553   a  is clicked. 
     As described, if the electric field reference mode is specified, the reference electric field strength “Pr (dBm)” can be inputted through the reference electric field strength inputting section for electric field reference mode  552   b . If the distance reference mode is specified, the reference distance “Dr (cm)” can be inputted through the reference distance inputting section  553   b , and the reference electric field strength “Pr (dBm)” can be inputted through the reference electric field strength inputting section for distance reference mode  553   c  can be inputted. If the reference electric field strength “Pr (dBm)” or the reference distance “Dr (cm)” is inputted through the inputting sections in step S 202 , the conversion formula in which the values are assigned to Formula 2 is used. If there is no such an input, the conversion formula in which the default reference electric field strength “0 (dBm)” and the default reference distance “100 (cm)” are assigned to Formula 2 is used. 
     After the input operation of step S 201 , the control device  300  turns to the standby state (step S 103 ). When the user clicks the measurement button  352   a  of the manual scanning section  352  or the start button  353   a  of the auto scanning section  353  (Yes judgment in step S 103 ), the process proceeds to the next process (step S 104 ). In step S 104 , a level specifying signal for specifying the output level with the specified value at the start is generated, a command to the RFID tag T 1  is constructed, and the level specifying signal and the command are transmitted. 
     When the process of step S 104  is terminated, the distance calculation processing section  312  converts the specified value at the start set by the output level setting section  305  to the distance between the antenna and the RFID tag T 1  when the predetermined antenna, which is used for the actual communication with the RFID tag T 1 , is connected to the reader/writer  200  (step S 202 ). In the present embodiment, the process of step S 202  is equivalent to an example of the converting step of the testing method in the present invention. 
     In the process of step S 202 , the output characteristic storage section  501  transfers the characteristic table corresponding to the reader/writer  200  specified in the process of step S 201  to the distance calculation processing section  505 , and the loss factor storage section  502  and the damping factor storage section  503  respectively transfer the loss factor in the second cable  42  and the damping factor in the stripline cell  100  inputted in the process of step S 102  to the distance calculation processing section  505 . The reference electric field/distance storage section  504  transfers the reference electric field strength “Pr (dBm)” and the reference distance “Dr (cm)” that are inputted in the process of step S 201 , or the default reference electric field strength “0 (dBm)” and the default reference distance “100 (cm)” to the distance calculation processing section  505 . Furthermore, the output level/command constructing section  306  transfers the specified value at the start to the distance calculation processing section  505 . 
     In the process of step S 202 , the electric power corresponding to the specified value at the start in the transferred characteristic table is first obtained. The total loss, which is the sum of the loss factor and the damping factor, is then subtracted from the electric power to obtain the electric field strength of the command signal transmitted by the stripline cell  100  and received by the RFID tag T 1 . 
     The obtained electric field strength is then converted to the distance between the antenna and the RFID tag T 1 . 
     The conversion is performed using Formula 2, and if the electric field reference mode is specified as the operation mode in step S 201 , the reference distance “Dr (cm)” in Formula 2 is fixed to the default reference distance “100 (cm)”. If the reference electric field strength “Pr (dBm)” for the electric field reference mode is inputted in step S 201 , the input value is assigned to the reference electric field strength “Pr (dBm)” in Formula 2. If there is no input, the default reference electric field strength “0 (dBm)” is assigned. 
     In the case the distance reference mode is specified as the operation mode in step S 201 , if the reference electric field strength “Pr (dBm)” and the reference distance “Dr (cm)” for the distance reference mode are inputted in step S 201 , the input values are assigned to the reference electric field strength “Pr (dBm)” and the reference distance “Dr (cm)” in Formula 2. If there is no input, the default reference electric field strength “0 (dBm)” and the default reference distance “100 (cm)” are assigned. 
     When the conversion formula is fixed through such assignments, the fixed conversion formula is used to convert the electric field strength to the distance. 
     When the conversion in step S 202  is terminated, the electric field strength obtained from the specified value at the start is numerically displayed on the strength displaying section  356   b  of the parameter setting section  551  and plotted on the graphic displaying section  362 . The distance displaying section  554  then numerically displays the distance between the antenna and the RFID tag T 1  converted from the specified value at the start. In the present embodiment, the distance displaying section  554  also displays the converted distance in parenthesis. 
     After the termination of the processes of step S 202  and step S 106 , the response transmitted by the reader/writer  200  is analyzed to determine, for example, the existence of the response from the RFID tag T 1 , and the analysis result is transmitted to the display processing section  313  (step S 107 ). 
     The display processing section  313  receives the analysis result (step S 108 ). If the analysis result indicates the existence of response (Yes judgment in step S 108 ), the display processing section  313  displays the existence of response on the text display screen  361  (step S 203 ). If the analysis result indicates no response (No judgment in step S 108 ), the display processing section  313  displays the no response on the text display screen  361  (step S 204 ). 
     As described below, in the process illustrated by the flow chart of  FIG. 14 , the process from step S 104  to step S 112  is repeated. In step S 204 , the display processing section  313  compares the analysis result in the current step S 107  and the analysis result in the previous step S 107 . If the analysis results are different, the display processing section  313  numerically displays the distance calculated in the current step S 202  on the text display screen  361  as the communication limit distance of the RFID tag T 1  to be processed, and the graphic displaying section  362  displays the output level (specified value) corresponding to the communication limit distance with the vertical line  362   a . In step S 204 , the display processing section  313  performs a similar comparison as in step S 109 , and if the results are different, the display processing section  313  numerically displays the distance calculated in the previous step S 202  as the communication limit distance and displays the output level (specified value) corresponding to the communication limit distance with the vertical line  362   a.    
     The control device  500  turns to the standby state when the display process of step S 203  or step S 204  is terminated (step S 111 ). 
     The standby state of step S 111  continues until the user again clicks the measurement button  352   a  (Yes judgment in step S 111 ) if the user has clicked the measurement button  352   a  of the manual scanning section  352  to remove the standby state of step S 103 . The standby state of step S 111  continues until the internal timer  304  informs a lapse of predetermined time (Yes judgment in step S 111 ) if the standby state of step S 103  has been removed by a click operation of the start button  353   a  of the auto scanning section  353 . 
     In the present embodiment, during the standby state of step S 111 , the user can click the electric field reference mode request button  552   a  or the distance reference mode request button  553   a  to, for example, request a change in the operation mode. 
     If the standby state is removed by the second click operation of the measurement button  352   a  or by the notification from the internal timer  304 , the output level setting section  305  increases or decreases the output level (specified value) by “1”, and the process returns to step S 104  (step S 112 ). 
     In the process illustrated by the flow chart of  FIG. 14 , the process from step S 104  to step S 112  is repeated until the termination condition in step S 113  described below is met. 
     In step S 113 , whether the specified value increased or decreased by “1” in step S 112  reaches a specified value of the end determined by the existence of the specification of trimming and the specified measurement direction is judged. If the specified value reaches the specified value of the end (Yes judgment in step S 113 ), the repetition is halted, and the process proceeds to the next process (step S 114 ). 
     On the other hand, if the specified value increased or decreased by “1” in step S 112  does not reach the specified value of the end (No judgment in step S 113 ), the process of steps S 205  and S 206  described below is executed, and the process from step S 104  to step S 112  is repeated. 
     In step S 205 , whether the user has, for example, requested a change in the operation mode during the standby state of step S 111  is determined. 
     If the user has not made a request (No judgment in step S 205 ), the process returns to the standby state of step S 111 . On the other hand, if the user has made a request (Yes judgment in step S 205 ), an input process corresponding to the requests by the user is executed (step S 206 ), and then the process returns to the standby state of step S 111 . 
     If there is, for example, a request change of the operation mode, the subsequent conversion in step S 202  is executed in the operation mode after the change using the reference electric field strength “Pr (dBm)” or the reference distance “Dr (cm)” inputted in step S 206 . In the present embodiment, the conversion before the change in the operation mode is also executed again when the operation mode is changed. If the communication limit distance has been displayed in the process of step S 203  or step S 204  before the change, the display is changed to the value based on the conversion executed again. 
     In step S 114 , the communication limit distance is saved automatically or manually through the manual saving section  355  based on the specification in step S 201 . When the display and the save of the communication limit distance in the process of step S 114  are completed, the process illustrated by the flow chart of  FIG. 14  is terminated. 
     In the process illustrated by the flow chart of  FIG. 14 , the electric field strength for conversion converted to the distance in step S 202  can be obtained from the characteristic table of the reader/writer  200 , the loss factor of the second cable  42 , and the damping factor of the stripline cell  100 , as described above. 
     In the present embodiment, the characteristic table, the loss factor, and the damping factor are based on the actual measurement. In the present embodiment, as for the characteristic table of the reader/writer  200 , the output characteristic storage section  501  stores a characteristic table actually measured in relation to the reader/writer  200 , and the characteristic table is used to obtain the electric field strength. On the other hand, the user inputs known values to the loss factor of the second cable  42  and the damping factor of the stripline cell  100 . Although it is presumed that measurement values are inputted as the values, there is a possibility that the values inputted by the user are not the measurement values of the second cable  42  and the stripline cell  100  of the RFID tag testing device  2 . For example, the values may be obtained from a cable and a stripline cell that are the same types as the second cable S 42  and the stripline cell  100  but that are different. In such a case, there may be a deviation between the electric field strength for conversion that is obtained from the characteristic table, loss factor, and the damping factor and that is displayed on the strength displaying section  356   b  and the electric field strength of the radio signal actually transmitted by the stripline cell  100 . If there is a deviation between the electric field strengths, the accuracy of the distance obtained by the conversion from the electric field strength, moreover, the accuracy of the communication limit distance obtained in the RFID tag testing device  2  is decreased. 
     The decrease in the accuracy of the communication limit distance will be described with specific examples. 
     For example, it is assumed that the communication limit distance of the RFID tag T 1  with the actual communication limit distance “110 (cm)” is measured through the series of processes. In this case, the electric field strength of the radio signal received by the RFID tag T 1  with the communication limit distance “110 (cm)” is assumed to be “−1.0 (dBm)” in the actual usage. 
     It is also assumed that the user has specified the electric field reference mode as the operation mode in step S 201  of  FIG. 14  and has not specifically inputted the reference electric field strength “Pr (dBm)”. As a result, the default reference electric field strength “10 (dBm)” is assigned to Formula 2 in the conversion of step S 202 . 
     It is further assumed that the electric field strength of the radio signal that the stripline cell  100  actually transmits when the electric field strength for conversion is “0 (dBm)” is “−1.0 (dBm)” in the RFID tag testing device  2  of  FIG. 7 . 
       FIG. 15  is a graph of a conversion relationship between the electric field strength and the distance using the default reference electric field strength “0 (dBm)”. 
     In a graph G 3  of  FIG. 15 , a line L 4  connecting white diamond marks illustrates the conversion relationship of Formula 2 using the default reference electric field strength “0 (dBm)”. The graph G 3  is a logarithmic graph displaying the distance transversely in the logarithmic scale. 
     In the conversion relationship illustrated by the line L 4 , the distance “100 (cm)” can be obtained when the electric field strength for conversion is “0 (dBm)”. However, with the assumptions described above, the actual electric field strength is “−1.0 (dBm)” that is the electric field strength of the radio signal received by the RFID tag T 1  when the communication limit distance is “110 (cm)”. Therefore, the communication limit distance obtained by the RFID tag testing device  2  is “100 (cm)” which is different from the actual communication limit distance “110 (cm)”. 
     In the present embodiment, such a deviation in the electric field strength can be eliminated by inputting an appropriate reference electric field strength “Pr (dBm)” or reference distance “Dr (cm)” in step S 201 . 
     A method of eliminating the deviation by inputting the appropriate reference electric field strength “Pr (dBm)” will be described first. 
     The method is performed in the electric field reference mode. 
     As described, the deviation between the electric field strength for conversion and the actual electric field strength is caused by the inaccuracy in the loss factor of the second cable  42  and the damping factor of the stripline cell  100  inputted by the user. The loss factor and the damping factor are fixed to obtain the electric field strength for conversion. The deviation occurs to every electric field strength for conversion in the same way. 
     The electric field strength for conversion “P (dBm)” is subtracted from the reference electric field strength “Pr (dBm)” in Formula 2. The deviation is the same for every electric field strength for conversion “P (dBm)”. Therefore, the electric field strength for conversion “P (dBm)” can be corrected to the actual electric field strength by inputting a value of the reference electric field strength “Pr (dBm)” such as to eliminate the value of deviation before conversion. 
     A specific value of deviation needs to be known to input the appropriate reference electric field strength “Pr (dBm)” for eliminating the value of deviation. However, in reality, the user often does not figure out the value of deviation when measuring the communication limit distance. In the present embodiment, a specific value of deviation can be obtained by the following procedure. 
     A standard dipole antenna for measuring the electric field strength is mounted on the stripline cell  100  in place of the RFID tag T 1 . The electric field reference mode is specified as the operation mode. The reference electric field strength “Pr (dBm)” is not particularly inputted, but instead, the default reference electric field strength “0 (dBm)” is used. The process is advanced by auto scan or manual scan until the display of the distance in the distance displaying section  554  becomes “100 (cm)”. The actual electric field strength of the radio signal transmitted by the stripline cell  100  is measured by the standard dipole antenna when the display becomes “100 (cm)”. 
     With the series of processes, the actual electric field strength is measured when the conversion to the default reference distance “100 (cm)” is performed. The electric field strength for conversion “P (dBm)” corresponding to the measured actual electric field strength is the default reference electric field strength “0 (dBm)”. The specific value of deviation can be obtained by calculating the difference between the actual electric field strength and the default reference electric field strength “0 (dBm)”. 
     The appropriate reference electric field strength “Pr (dBm)” for eliminating the value of deviation can be obtained by adding the obtained value of deviation to the default reference electric field strength “0 (dBm)”. 
     For example, with the assumptions described above, the actual electric field strength when the conversion to the default reference distance “100 (cm)” is performed is “−1.0 (dBm)”. Therefore, the value of deviation is “1.0 (dBm)”, which is the difference between the two. The value of deviation “1.0 (dBm)” is added to the default reference electric field strength “0 (dBm)”, and the appropriate reference electric field strength “1.0 (dBm)” is obtained. 
     The appropriate reference electric field strength “Pr (dBm)” obtained this way is inputted in step S 201  of  FIG. 14  to properly eliminate the value of deviation “1.0 (dBm)” during the conversion to the distance. 
     In the graph G 3  of  FIG. 15 , the line L 4  connecting the white diamond marks illustrates a conversion relationship (conversion relationship at the beginning) of Formula 2 using the default reference electric strength “0 (dBm)” and the default reference distance “100 (cm)”. A line L 5  formed by dashed line illustrates a conversion relationship (modified conversion relationship) of Formula 2 using the appropriate reference electric field strength “1.0 (dBm)”. As can be seen by comparing the two lines, the modified conversion relationship is equivalent to the conversion relationship at the beginning moved in parallel in an arrow A direction by the value of deviation (“1.0 (dBm)” in the example here). This is also equivalent to rereading the distance obtained from the conversion relationship at the beginning after shifting the transverse scale of the graph G 3  in a direction illustrated by an arrow B. 
     In this way, the deviation between the electric field strength for conversion and the actual electric field strength is eliminated with calculation in the measurement process of the communication limit distance executed by inputting the appropriate reference electric field strength “Pr (dBm)” in step S 201  of  FIG. 14 . 
     With the assumptions described above, the actual communication limit distance is “110 (cm)”, and the electric field strength of the radio signal received by the RFID tag T 1  with the communication limit distance “110 (cm)” is “−1.0 (dBm)”. The actual electric field strength when the electric field strength for conversion is “0 (dBm)” is “−1.0 (dBm)”. In the present embodiment, the electric field strength “0 (dBm)” that is converted to “100 (cm)” with the conversion relationship at the beginning is converted to “110 (cm)” by the modified conversion relationship. In this way, the communication limit distance can be obtained correctly as “110 (cm)”, which has been wrongly obtained as “100 (cm)” in the measurement process using the conversion relationship at the beginning. 
     As described, in the method of eliminating the deviation by inputting the appropriate reference electric field strength “Pr (dBm)”, the user measures a specific value of deviation through the series of processes to obtain the appropriate reference electric field strength “Pr (dBm)” for eliminating the value of deviation prior to the measurement process of the communication limit distance of the RFID tag T 1 . Upon the measurement process of the communication limit distance of the RFID tag T 1 , the user can obtain an accurate communication limit distance by specifying the electric field reference mode as the operation mode and inputting the appropriate reference electric field strength “Pr (dBm)”. 
     A method of eliminating the deviation by inputting the appropriate reference distance “Dr (cm)” and the appropriate reference electric field strength “Pr (dBm)” will now be described. 
     The method is performed in the distance reference mode. 
     In the distance reference mode, the user inputs the reference distance “Dr (cm)” and the reference electric field strength “Pr (dBm)” that needs to be converted to the reference distance “Dr (cm)” in step S 201  of  FIG. 14 . If appropriate values are inputted in which it is definitely known that the reference distance “Dr (cm)” and the reference electric field strength “Pr (dBm)” correspond, a highly accurate conversion in which the deviation is eliminated can be performed, even if the electric field strength for conversion and the actual electric field strength are deviated. 
     In the present embodiment, the appropriate reference distance “Dr (cm)” and the appropriate reference electric field strength “Pr (dBm)” that are definitely known to correspond are obtained by the following process prior to the measurement of the actual communication limit distance. 
     A standard RFID tag T 1  is first prepared in which the communication limit distance is already known, and the measurement process of the communication limit distance of the standard RFID tag T 1  is executed. In step S 201  of  FIG. 14 , the distance reference mode is specified as the operation mode, the reference distance “Dr (cm)” and the reference electric field strength “Pr (dBm)” are not inputted, and the default values are used in the process. The electric field strength for conversion displayed on the strength displaying section  356   b  when the communication limit distance is displayed on the text display screen  361  in the process is recorded. The recorded electric field strength for conversion is the minimum electric field strength that the standard RFID tag T 1  can react and is an electric field strength that needs to be converted to the actual communication limit distance that is already known. Thus, it can be said that the actual communication limit distance that is already known and the electric field strength for conversion are the distance and the electric field strength that definitely correspond. 
     In the present embodiment, such a distance and an electric field strength obtained by the process using the standard RFID tag T 1  are used as the appropriate reference distance “Dr (cm)” and the appropriate reference electric field strength “Pr (dBm)”. 
     The elimination of the deviation in the distance reference mode will be further described in detail with a specific example. 
     It is assumed that the actual communication limit distance of the standard RFID tag T 1  is “140 (cm)” and the electric field strength for conversion that is obtained in the process and that definitely corresponds to the communication limit distance “140 (cm)” is “−5.0 (dBm)”. 
       FIG. 16  depicts how the deviation is eliminated in the distance reference mode. 
     As in the graph G 3  illustrated in  FIG. 15 , a graph G 4  illustrated in  FIG. 16  is a logarithmic graph in which the distance is displayed transversely in the logarithmic scale. As in  FIG. 15 , the graph G 4  depicts, with the line L 4  connecting the white diamond marks, a conversion relationship expressed by the conversion formula before modification in which the reference electric field strength “Pr (dBm)” is “0 (dBm)” and the reference distance “Dr (cm)” is “100 (cm)”. 
     As can be seen from the line L 4 , the communication limit distance displayed on the text display screen  361  when the electric field strength for conversion is “−5.0 (dBm)” is “170 (cm)”, which is “30 (cm)” longer than the communication limit distance “140 (cm)” that is already known. The user records the electric field strength for conversion “−5.0 (dBm)” displayed on the strength displaying section  356   b  when the communication limit distance “170 (cm)” is displayed. 
     In the measurement process of the actual communication limit distance, the distance reference mode is specified as the operation mode, the communication limit distance “140 (cm)” of the standard RFID tag T 1  is inputted as the appropriate reference distance “Dr (cm)”, and the electric field strength for conversion “−5.0 (dBm)” recorded in the process is inputted as the appropriate reference electric field strength “Pr (dBm)” in step S 201  of  FIG. 14 . 
     The graph G 4  of  FIG. 16  depicts a conversion relationship (modified conversion relationship) expressed by Formula 2 assigned with the appropriate values with a line L 6  formed by dashed line. In the conversion relationship illustrated by the line L 6  formed by dashed line, the electric field strength for conversion “−5.0 (dBm)” is converted to the distance “140 (cm)” as described. The modified conversion relationship illustrated by the line L 6  formed by dashed line is equivalent to the one in which the conversion relationship (conversion relationship before modification) illustrated by the line L 4  is moved in parallel in an arrow C direction for a value f of deviation of the electric field strength at the distance “140 (cm)”. In this way, by using the distance and the electric field strength that are definitely known to correspond as the reference distance and the reference electric field strength, a highly accurate conversion in which the deviation is eliminated can be performed, even if the electric field strength for conversion and the actual electric field strength are deviated. 
     As described, in the present embodiment, the deviation between the electric field strength for conversion and the actual electric field strength can be eliminated by using the appropriate reference electric field strength in the electric field reference mode, and the deviation can be eliminated by using the appropriate reference distance and the appropriate reference electric field strength in the distance reference mode. 
     In the present embodiment, a change in the operation mode can be requested in the waiting time of step S 111  of  FIG. 14 . If the operation mode is changed after the communication limit distance is displayed, the communication limit distance is changed to a value based on the conversion in the operation mode after the change. As a result, when, for example, the communication limit distance is obtained in the electric field reference mode based on the appropriate reference electric field strength, the accuracy of the communication limit distance can be checked by measurement by changing the operation mode to the distance reference mode, causing the communication limit distance in the distance reference mode to be displayed based on the appropriate reference distance and the appropriate reference electric field strength, and comparing the communication limit distances in two operation modes. 
     As described, according to the RFID tag testing device  2  of the present embodiment, the communication limit distance of the RFID tag T 1  can be easily obtained with high accuracy as in the RFID tag testing device  1  of the first embodiment. Furthermore, the communication limit distance can be obtained with higher accuracy by using the appropriate reference electric field strength in the electric field reference mode or using the appropriate reference distance and the appropriate reference electric field strength in the distance reference mode. 
     Although the stripline cell  100  has been illustrated as an example of the transmitting section of the testing device in the present invention, the transmitting section is not limited to this. The transmitting section may be, for example, an antenna used for the actual communication with the RFID tag. In that case, the electric field strength table as an example of the characteristic table of the testing device in the present invention describes, for example, a one-to-one correspondence between the multiple specific values of the output levels with respective to the reader/writer and the electric field strengths corresponding to the specified values at a point that is “1(m)” away from the antenna. When using the antenna as the transmitting section, for example, the characteristic table described with the output characteristics of the reader/writer may be used as in the second embodiment, and the user may numerically input the antenna gain of the antenna or the spatial damping factor at the point that is “1(m)” away from the antenna. 
     According to the present invention, the electric field strength of the radio signal received by the electronic device from the output level specified by the specifying section can be obtained, and the electric field strength is further converted to the distance between the antenna and the electronic device. Therefore, the communication limit distance of the electronic device can be obtained by a simple operation such as gradually raising the output level while the reaction checking section checking the existence of the reaction without moving the electronic device. The accuracy of the communication limit distance obtained by the operation depends on the accuracy of obtaining the electric field strength from the output level and the accuracy of converting from the electric field strength to the distance. The conversion from the electric field strength to the distance can be accurately performed in accordance with, for example, general physical laws denoting the correspondence between the propagation distance of radio wave and the electric field strength. Therefore, the accuracy of the communication limit distance largely depends on how accurately the electric field strength of the radio signal received by the electronic device from the output level specified by the specifying section can be obtained. According to the present invention, the electric field strength can be obtained based on the unique output characteristics included in the signal outputting section. Thus, significantly accurate electric field strength can be obtained, and as a result, the converting section can obtain a highly accurate communication limit distance. 
     Therefore, according to the testing device and the testing method in the present invention, the communication limit distance of the electronic device that receives and reacts to the radio signal can be easily obtained with high accuracy. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.