Abstract:
A light source having a lamp for generating light generates a lamp on signal at an output terminal thereof when the lamp is lit. A lamp life meter is connected to the light source for detecting the time that the lamp has been lit. The lamp life meter includes a housing having at least one contact terminal adapted to be coupled to the output terminal of the light source, a clock generator located in the housing and generating clock signals, a counter located in the housing and counting the clock signals whenever the clock on signal indicates that the lamp is on and a display mounted in the housing for displaying an indication of the time the lamp has been turned on.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a lamp life meter for displaying the remaining life of a lamp that emits light to be provided to an endoscope. 
     In recent years, endoscopes have been widely used in both medical and industrial fields. Such endoscopes typically include a light-guiding means which guides light emitted from an external light source to the endoscope to the distal end of the insertion section of the endoscope. This light illuminates a body cavity or the inside of a machine to be viewed with the endoscope. 
     One typical light source is a xenon lamp (or an iodine lamp or metal halide lamp) which is installed in an endoscope light source unit to provide illuminating light to the endoscope. The life of such a lamp is limited and must be replaced after its life expectancy has expired. 
     To avoid the possibility that the lamp will burn out or generate insufficient light while the endoscope is in use (which would hinder a correct diagnosis), it is necessary to correctly notify the user when the life of the lamp will end. Traditionally, a conducting time counting meter (hereinafter referred to as “lamp life meter”) has been used to achieve this result. 
     FIGS.  16 (A),  16 (B) and  17  show a traditional lamp life meter  81 . FIGS.  16 (A) and  16 (B) are front and side views of the traditional lamp life meter  81 , which is covered with a resin case and has a graded scale  82 . The graded scale illustrated in the drawing can count a maximum of 500 hours. A positive input terminal  84  and a negative input terminal  85  extend from the lower part of the main body of the lamp life meter  81  and energize the lamp life meter  81 . 
     FIG. 17 shows the principle of operation of the lamp life meter  81 . The traditional lamp life meter  81  includes a glass tube  86  housing mercury  87  and an electrolyte solution  88 . When a direct-current voltage is placed between the electrodes (input terminals  84  and  85 ), mercury  87  is electrolytically extracted from the anode side to the cathode side via the electrolyte solution  88 , and the electrolyte solution  88  is moved from the cathode side to the anode side. 
     Since the distance the electrolyte solution moves is proportional to the quantity of electricity flowing, the total conducting time (i.e., the time that current has been flowing through the lamp and therefore through the terminals  84 ,  85 ) can be shown, assuming that a constant current flows through terminals  84  and  85 . 
     With the traditional lamp life meter  81 , a circuit is provided in the light source unit to provide a minimal-ampere (15 μA) direct-current voltage, and the light source unit&#39;s main body and the lamp life meter  81  are connected with a socket so that it is detachable. 
     The traditional light source unit&#39;s main body has the same structure as the light source unit&#39;s main body illustrated in FIG. 2 described below. 
     The lamp life meter  81  is energized through the lamp-lighting circuit  12  (FIG.  2 ). When the lamp  11  is lit, a current of approximately 15 μA, which is suitable for driving the lamp life meter  81 , is provided to the lamp life meter socket  6   a  (and/or  6   b ). 
     Traditional lamp life meters of the foregoing type have the following advantages: 
     a. They are easy to use; 
     b. They are compact; 
     c. They are relatively low-priced; and 
     d. They reliably count the conduction time (and therefore the time that the lamp has been lit) and simply display it. 
     Generally, lamps used for the endoscope light source unit are consumed over time. Additionally, the quantity of light (the quantity of light shot from the distal end of the endoscope) is also reduced over time. Generally, the end of the lamp life means that; there is an unsatisfactory reduction in the quantity of light or that the lamp does not light. 
     A lamp life meter is traditionally installed on the endoscope light source unit, so that the remaining lamp life can be confirmed before use, and so that the lamp can be replaced with a new one when an insufficient lamp life remains. 
     While mercury having a high purity of 99.99% is used in traditional lamp life meters, the number of manufacturers producing such high-level mercury has been reduced. Additionally, some of mercury refineries have been closed, making it difficult to procure the required mercury used in traditional lamp life meters. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is intended to act as a substitute for the traditional lamp life meters and serves the same functions without the use of mercury. Preferably, the lamp life meter of the present invention is compatible with endoscope light source units designed to accept the traditional lamp life meter. 
     A lamp life meter compatible with traditional lamp life meters can be provided by realizing a lamp life meter detachably attached to a lamp life meter socket that can place a minimal-ampere direct-current voltage between two terminals when in an endoscope light source unit comprising a lamp emitting light for viewing through an endoscope and a lamp-lighting circuit providing lamp-lighting power for lighting said lamp, said lamp is lit, wherein a means is provided to display the lamp life by detecting the time for which said direct-current voltage is placed between said two terminals of said lamp life meter socket. 
     The invention is directed towards a lamp life meter adapted to be detachably coupled to a light source of the type which generates a lamp on signal indicating that a lamp of said light source is turned on. The lamp life meter detects the total length of time that the lamp is turned on. The lamp life meter comprises: 
     a housing having at least one contact terminal adapted to be coupled to one or more output terminals of said light source, said lamp on signal appearing on one or more of said output terminals when the lamp is on; 
     a clock generator located in said housing and generating clock signals; 
     a counter located in said housing and counting said clock signals whenever said lamp or signal indicates that said lamp is on; and 
     a display mounted in said housing for displaying an indication of the time said lamp has been turned on. 
     The lamp life meter preferably includes a power source (a battery) located in the housing for powering the lamp life meter. A switch is provided for preventing power from being applied from the battery to said clock, counter and display. 
     The switch preferably comprises an insulating tab moveable between a first position wherein it prevents power from the battery from being applied to the clock, counter and display and a second position wherein it permits power from the battery to be applied to the clock, counter and display. 
     The tab is preferably slidable between the first and second positions and has an indication (e.g. an arrow head) formed therein indicating the direction the tab must be moved to bring it from the first to the second position. In some embodiments the tab has an insulating section and a conducting section. The insulating section is located between the battery and the clock, counter and display when the tab is in the first position. The conducting section is located between the battery and clock, counter and display when the tab is in the second position. The conducting section may have a conductive material formed over an insulating substrate or may be a hole formed in the tab. The tab can include a perforated portion which can be torn off from the remainder of said tab. 
     The display preferably includes a plurality of LED&#39;s. The pattern of the LED&#39;s which are lit indicate the time period that said light has been lit. The LED&#39;s preferably flash when they are lit to save energy. 
     The counter is preferably a programmed microprocessor which is programmed to carry out one or more tests concerning the operation of the lamp life meter. These tests can include a test to determine if the display is working properly and a test to determine if the counter is working properly. 
     The microprocessor preferably backs up the count of the counter to a non-volatile memory when the lamp on signal is removed from the at least one contact terminal. The microprocessor preferably switches to a sleep mode when the lamp on signal does not appear at the at least one contact terminal. 
     The invention is also directed to the combination of a light source having a lamp for generating light, the light source generating a lamp on signal at an output terminal thereof, and the lamp life meter described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. 
     FIG. 1 is a perspective view of an endoscope light source unit incorporating a lamp life meter according to a first embodiment of the present invention. 
     FIG. 2 is a schematic view showing the general configuration of the endoscope light source unit of FIG.  1 . 
     FIG.  3 (A) is a top view of the lamp life meter of FIG.  1 . 
     FIG.  3 (B) is a side view of the lamp life meter. 
     FIG. 4 is a block diagram showing the general configuration of the electrical system of the lamp life meter. 
     FIG.  5 (A) is a front, sectional view of the lamp life meter. 
     FIG.  5 (B) is a side, sectional view of the lamp life meter. 
     FIG.  5 (C) is a bottom view of the lamp life meter. 
     FIG.  5 (D) is a top sectional view of the lamp life meter of wherein an insulating tab  44  is located within the lamp life meter. 
     FIG.  5 (E) is a side sectional view of the lamp life meter wherein the insulating tab is housed within the meter. 
     FIG.  6 (A) is a top view of the battery holder forming part of the lamp life meter of FIG.  1 . 
     FIG.  6 (B) is a sectional side view of the battery holder. 
     FIG.  6 (C) is a top view of the battery holder with the insulating tab in place. 
     FIG.  7 (A) is a top sectional view of the lamp life meter with the insulating tab in place. 
     FIG.  7 (B) is a side sectional view of the lamp life meter with the insulating tap in place. 
     FIG.  7 (C) is an alternative embodiment of the insulating tab. 
     FIG.  7 (D) is a further alternative embodiment of the insulating tab. 
     FIG.  7 (E) is yet a further alternative embodiment of the insulating tab. 
     FIG. 8 is a circuit diagram of one possible electronic circuit to be used as pert of the lamp lighting circuit of FIG.  1 . 
     FIG. 9 is a wiring diagram showing one possible circuit implementing the lamp life meter using a chip microprocessor. 
     FIG. 10 is a block diagram showing the internal configuration of the chip microprocessor of FIG.  9 . 
     FIG. 11 is a timing diagram showing signals used to drive the LCD display of the lamp life meter. 
     FIG. 12 is a chart showing the preferred mode of operation of the LCD display during the normal mode of operation. 
     FIG. 13 is a chart showing the preferred operation of the LCD display during a test mode of the LCD display. 
     FIG. 14 is a flow chart showing the main routine carried out by the microprocessor of FIG.  9 . 
     FIG. 15 is a flow chart a timer interrupted routine carried out by the microprocessor of FIG.  9 . 
     FIG.  16 (A) is a top view of a prior art lamp life meter. 
     FIG.  16 (B) is a side view of the prior art lamp life meter. 
     FIG. 17 is a schematic sectional view of the prior art lamp life meter. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring further to the drawings wherein like numerals indicate like elements, there is shown in FIG. 1 an endoscope light source unit  1  and a lamp life meter  3  constructed in accordance with the principles of the present invention. The lamp life meter  3  is detachably attached to the light source unit&#39;s main body  2 . 
     On the front face of the light source unit&#39;s main body  2 , is arranged a connector support  4  for detachably receiving the light guide connector  5  of an endoscope (not shown). When the light guide connector  5  is connected as shown in FIG. 2, illuminating light can be provided. 
     A lamp life meter socket  6   a  to which the lamp life meter  3  can be mounted is provided, for example, on the lower part of the front face of the light source unit&#39;s main body  2 . A lamp life meter socket  6   b  to which the lamp life meter  3  can be mounted may also be provided on the reverse face of the light source unit&#39;s main body  2  either in lieu of, or in addition to, the lamp life meter socket  6   a . The light source unit&#39;s main body  2  has the same configuration as that of the traditional light source unit&#39;s main body  2 . The sockets  6   a  and  6   b  can receive either the traditional lamp life meter  81  or the lamp life meter  3  of the present invention. 
     As shown in FIG. 2, the endoscope light source unit  1  comprises a lamp  11  (a xenon lamp, for example) emitting illuminating light to be provided to the light guide connector  5  connected to the connector support  4 , a lamp-lighting circuit  12  providing lamp-lighting power for lighting the lamp  11 , a power circuit  13  for energizing various circuits including the lamp-lighting circuit  12 , a display panel  14  constituted of various switches and display means (LED display equipment, etc.) arranged on the front panel section of the light source unit&#39;s main body  2 , a control unit  15  for switching the lamp  11  on and off and controlling the brightness of the lamp according to signals received from the display panel  14  via the lamp-lighting circuit  12 , a condensing lens  16  for condensing illuminating light emitted from the lamp  11  and providing it to the light guide connector  5  of the endoscope, a diaphragm  17  for controlling the quantity of illuminating light to be provided to the light guide connector  5 , a diaphragm-driving circuit  18  for adjusting the opening of the diaphragm  17 , a cooling fan  19  for radiating (cooling) heat generated by the lamp  11 , and a lamp life meter socket  6   a  (or  6   b ) connected to the lamp-lighting circuit  12 , wherein commercial electrical power can be provided to the power circuit  13  via the AC plug  20 . 
     The lamp-lighting circuit  12  includes a circuit that detects the fact that the lamp  11  is on, and outputs signals to the lamp life meter socket  6   a  (or  6   b ) only during the period that the light is lit. In the following description, it is assumed that only the lamp life meter socket  6   a  is provided. 
     The lamp life meter is energized through the lamp-lighting circuit  12  (which is controlled by the control unit  15 ) when the lamp  11  is lit. During this time period, a current of approximately 15 μA (which is suitable for driving the lamp life meter  3 ) is provided to the lamp life meter socket  6   a.    
     As shown in FIGS.  3 (A) and  3 (B), lamp life meter  3  is generally rectangular in shape; its upper face (surface, front face) and bottom face (reverse face) being covered with an upper cover  21  and a lower cover  22 , respectively. Its dimensions and appearance are substantially the same as the traditional lamp life meter  81 . A positive (+) input terminal  24  and a negative (−) input terminal  25  are arranged on the reverse face of the lamp life meter  3 . The shape of and the distance between these input terminals  24  and  25  are identical to those of the traditional lamp life meter  81 . The lamp life meter  3  can be inserted into the lamp life meter socket  6   a  in lieu of the traditional lamp life meter  81 . 
     A liquid crystal display device (LCD)  26  is provided as a display means for showing the remaining lifetime of the lamp based on the total time that the lamp  11  has been lit. 
     The LCD  26  is preferably arranged on a rectangular window situated around the center of the upper cover  21  and may take the form of a bar display section  27  which changes, for example, after every 50-hour use. 
     According to the present embodiment, the next bar blinks every 50 hours from the start of counting the use of the lamp until the lamp has been used for a total of 300 hours. The next two bars blink every 100 hours from 300-hour use to 500-hour use. The highest-rank bar blinks after 500-hours of use. While such intervals are described by way of example, any desired set of intervals and any desired display may be provided. 
     FIG. 4 is a schematic view of the electric system of the lamp life meter  3 . It includes a CPU that counts the total time that the lamp  11  has been lit based on signals it receives from input terminals  24  and  25 , and outputs display signals to the LCD  26 , an oscillator (OSC)  32 , for example, a crystal oscillator, that produces clock signals with the lapse of time that are counted by the CPU  31  when the lamp on signal from the light source unit  1  appears on input terminals, an LCD (LCD panel in FIG. 5)  26  for showing the total time that the lamp  11  has been used, a battery  33  that provides power to drive the CPU  31  and back up the elapsed time, and input terminals  24  and  25  for receiving lamp-lighting signals from the light source unit&#39;s main body  2 . 
     The CPU  31  is preferably a chip microprocessor on which various input and output ports and memories are mounted; and lamp-lighting signals are applied to an input port, and the LCD  26  is connected to an output port. The terminals  34  and  35  are connected to the CPU  31 . To check operation of the lamp life meter  3  according to the present embodiment: it is possible to obtain access to the lamp life meter  3  from the outside. 
     The traditional lamp life meter  81  is activated by a minimal-ampere current of approximately 15 μA, and only a current of up to 15 μA can be output from the lamp life meter socket  6   a  of the light source unit&#39;s main body  2 . 
     In order to be compatible with light sources designed for use with the traditional lamp life meter  81 , it is preferred that the lamp life meter  3  meet the following conditions: 
     a. The total time is counted as soon as the lamp-on signal (of around 15 μA) is output from the light source unit (i.e., the signal appearing at socket  6   a ); 
     b. The total elapsed time is shown while the total elapsed time is being counted; 
     c. When the lamp-on signal (5 μA) is interrupted, counting of the elapsed time is stopped, and the total elapsed time at that point is backed up; 
     d. When the lamp-one signal (15 μA) is output again from the light source unit, counting of the total elapsed time is restarted from the total elapsed time figure backed up when the lamp-on signal was previously stopped; 
     e. Only an elapsed time of a predetermined number of hours (e.g., 500 hours) can be counted, and when that number of hours is exceeded, the highest of the LCD bar display section  27  should be displayed; 
     f. The life of the battery should be greater than the predetermined number of hours (e.g., 500 hours) in the continuous operation state for counting the total time; and the life of the LCD should exceed two years in the stand-by state. Like all of the listed requirements, this requirement is not absolute because it depends on the particular characteristics of the light source unit; 
     g. Means should be provided to ensure that power is not applied to the lamp life meter  83  before its initial use so that the battery will not be consumed; 
     h. The dimensions and appearance are almost the same as those of the traditional lamp life meter. 
     In order to have these desired attributes, the present embodiment is modular in design, uses a button-type battery  33  as the power for driving circuits and is configured as follows. 
     The CPU  31  is of the low power consumption type: 50 to 30 μA when in the operation mode, while 2 to 1 μA when in the sleep mode (stand-by mode). In addition, each port of the CPU uses a pull-down circuit in order to restrain the power consumption from increasing due to the presence of a pull-up resistor, for example. An LCD  26  using 0.5 to 1 μA is preferably used. 
     In order to ensure that power is not applied to the CPU before the lamp life meter  3  is used with a lamp source unit  1 , an insulating means is provided between a terminal of the battery  33  and a terminal of the battery holder. 
     Referring to FIGS.  5 (A)- 5 (E), the detailed construction of the present embodiment will be described. 
     As shown in these figures, an upper cover  21  on the display face side and the lower cover  22  on the side for insertion into the socket  6   a  can be fit into one another with a single motion to form an outer case. 
     An opening is formed in the upper cover  21  so that the bar display section  27  (FIG. 4) of the LCD panel  26  can be seen. Below the opening is a circuit board  41  on which LCD panel  26 , a conductive rubber (for example, Zebra™ Rubber)  40 , electrical parts, etc., are installed. 
     Various other parts such as CPU  31 , oscillator  32 , battery holder  42 , batteries  33 , contact pins (input terminals  24  and  25 ), resistors, and a capacitor are formed on circuit board  41 . A pattern for electrically connecting the LCD panel  26 , the conductive rubber  40 , and the output port of the CPU  31 , are formed on the circuit board  41  which can be connected at the same time when the upper cover  21  and the lower cover  22  are fit together in a single motion. 
     On the lower cover  22 , is arranged an check hole  43  (FIG.  5 (C)) through which access can be obtained to check terminals  34  and  35  which are used for checking operation of the lamp life meter  3  during the manufacturing process or when the lamp life meter  3  is serviced. 
     As shown in FIG.  5 (E), the battery  33  is prevented from being consumed by a film-like insulating tape  44  located between the battery  33  and the battery holder  42  before the lamp life meter  3  is installed in the light source unit  1 . The insulating tape  44  operates as a switch which is moveable between a first position wherein power is applied to the circuits of the lamp life meter (including the CPU, the display and the oscillator) and a second position wherein the power is cut off. 
     FIGS.  6 (A)- 6 (C) show the details of the battery holder  42  and the power insulation structure. FIG.  6 (A) is a top view of the battery holder  42 ; FIG.  6 (B) is a longitudinal sectional view of the battery holder portion; and FIG.  6 (C) shows how the insulating tape  44  covers the contacts  52   a ,  52   b  of the battery holder  42  (thereby insulating the contacts  52   a  from the terminal of the battery  33 ) while the insulating tape is in the illustrated position. 
     The battery holder  42  comprises a main body  51  designed to accommodate two batteries  33  and electrode contacts  52   a  and  52   b . Contacts  52   a ,  52   b  are preferably spring type contacts. One pair of contacts  52   a  are coupled to a terminal  53  which is connected to a corresponding conductor on the circuit board  41  and a second pair of contacts  52   a  are coupled to a terminal  54  which is connected to a corresponding conductor on circuit board  41 . Such structure allows an automatic substrate installation machine to mount the battery holder  42  on the circuit board  41 . 
     A tape insertion hole  54  into which the insulating tape  44  can be inserted between the battery  33  and the electrode spring  52   a  (and from which it can be extracted afterwards) is formed on the main body  51  of the battery holder  42 . The position of the insulating tape relative to one of the batteries  33  and the battery holder  42  is shown in FIGS.  7 (A) and  7 (B). In this embodiment, the entire insulating tape  44  is formed of an insulating material and must be removed from the lamp life meter  3  in order to permit battery power to be applied to the CPU. 
     Alternative structures of insulating tape  44  are shown in FIGS.  7 (C)- 7 (E). In each of these examples, the insulating tape  44  has a conducting means, such as an opening  55  or conducting member  56 , in the center of the tape which is itself constituted of insulating material. When the tape is moved to a position wherein the conducting means is located between the battery terminal and the terminals  52   a , electricity can flow between the electrode terminals  52   a  and the battery  33 . 
     The end of the insulating tape  44  may take various shapes. The square shape  57  shown in FIG.  7 (C) can be easily grabbed by hand. The arrow shape  58  shows the direction that the tape must be moved. Changing the color of the tape (not illustrated) makes it easy to judge whether the tape is inserted. 
     As shown in FIG.  7 (E), the insulating tape  44  may be perforated at a location along which it can be torn. 
     The insulating means shown in FIG.  7 (C)- 7 (E) make it possible to check the operation of the lamp life meter  3  at the factory without removing the insulating tape. Using any of these embodiments, the electrodes of the battery  33  and the terminals  52   a  are temporarily brought into conduction through the opening  55  of the insulating tape  44  (or through the conductive section  56 ) to check operation of the internal circuit during the manufacturing process of the lamp life meter  3 . Since several test programs for operation test modes are stored in advance in the memory (for example, the PROM  61  in FIG. 10) embedded in the CPU  31 , a test mode can be selected by choosing a test terminal of the CPU  31 . After an operation test mode is selected, the testing operation is finished. 
     Next, the insulating tape  44  is extracted, and stopped in some insulating area other than the opening  55  or the conductive portion  56 . In such a state, the lamp life meter  3  is shut off from the power, and all is reset. 
     As shown in FIG.  7 (E), a perforation may be provided on the insulating tape. After the insulating tape  44  is extracted, and stopped in some insulating area other than the opening  55 , the insulating tape  44  can be torn with the conductive member  56  to prevent a user&#39;s wrong manipulation from causing a current to be passed. 
     The CPU controls the operation of the lamp life meter  3  in accordance with a prestored operation program. In accordance with the preferred program, the lamp life meter  3  operates and the LCD  26  starts only when the lamp-lighting signals is applied to the input terminals  24  and  25 , while the sleep mode (stand-by state) is selected to save the power consumption when the lamp-lighting signal is shut off. Moreover, the LCD  26  is not continuously lit, but blinks during operation to save power consumption. 
     The life meter  3  is detachably connected to the lamp life meter socket of the light source unit&#39;s main body  2  shown in FIG. 2, and power suitable for driving the lamp life meter  3  is provided to the lamp life meter socket  6   a  through the power circuit  13  when the lamp  11  is lit. 
     FIG. 8 shows the one possible embodiment of the lamp-lighting circuit  12  used to light a xenon lamp used as the lamp  11 . This circuit is of the PMW and the switching regulator type, which feeds back the current flowing to the lamp  11 , and controls the lighting of the xenon lamp with a constant current. 
     An input AC power signal is commutated by the diode DB 1 , and smoothed by the smoothing capacitors C 1  and C 2 . The PWM control circuit IC IC 1  is connected to the gate of the switching transistor TR 1  via the resistor R 1 , and the first winding of the inverter transformer T 1  is connected to its source drain side. The PWM control circuit IC 1  is connected to the photo-coupler PC 1 , and the phototransistor of the photo-coupler PC 1  is connected of the end of the power source via the resistor R 2 . 
     As the configuration of the second circuit, smoothing capacitors C 3  and C 4 , smoothing diodes D 1  and D 2 , an inductor L 1 , etc. are arranged. The series circuit comprising the resistor R 4  and the capacitor C 5  is provided to supply a superimposed current for lighting the lamp  11  in an efficient manner. A coil T 2 , for applying a high voltage to the lamp  11  is connected to the igniter. 
     When the lamp  11  is lit, a voltage is generated between the ends of the current sensing resistor R 10  to drive the photo-coupler PC 1  via the photo-coupler-driving circuit IC 2  through which the control circuit IC 1  is fed back to light the lamp  11  by the constant current. Resistors R 5  through R 9  are connected to IC 2 . 
     The power for the lamp life meter  3  is provided to socket  6   a  by comparator IC 3  via the resistor R 15  used to control the current. When the lamp  11  is lit, the voltage generated between the ends of the current sensing resistor R 10  is input to the noninverting input terminal of the comparator IC 3  via the resistor  11 , and is compared with the reference voltage located between resistors R 12  and R 13  to change the output from the comparator IC 3  from the low “L” level to the high “H” level. 
     When at the “H” level, the resistor R 15  connected in series with the end of the power source via the resistor R 14  can provide the lamp life meter socket  6   a  with a current of approximately 15 μA for driving the traditional lamp life meter. 
     One possible circuit configuration for the lamp life meter  3  is shown in FIG.  9 . The primary component of the lamp life meter  3  is CPU  31 , a chip microprocessor (preferably a PIC16LC554) that counts the total time that the lamp  11  has been lit, and drives the LCD  26  to display that time. A capacitor  11  is placed between the power source VDD and ground. 
     The liquid crystal display panel, LCD  26 , is connected to the pad of W 1 , via the conductive rubber (e.g., Zebra™ rubber). 
     The battery  33 , comprising two silver oxide cells located in the battery holder  42 , is connected to each pad W 5  through W 8  to provide a voltage of 3.1 volts. The voltage of 3.1 volts is dropped by the back-flow preventive diode D 4  to around 2.8 volts, which is provided as the power source VDD for the microprocessor PIC. 
     When a voltage of +5 volts with an impedance of 240 KΩ (the signal provided from the lamp life meter socket  6   a  of the light source unit&#39;s main body  2 ) is input to terminal J 1  (MAIN LAMP ON), a voltage of 2.2 to 2.8 volts (obtained through a voltage drop through the resistor R 21  and the output circuit on the side of the light source unit&#39;s main body  2 ) is input to the  7  pin of the microprocessor PIC. 
     The pull-down resistors R 21  and R 22  are arranged to stabilize the input pins at ground potential when no input is applied. This is done to prevent the battery  33  from being consumed. 
     The crystal oscillator Y 1 , can be used as the oscillator  32  to produce clock signals for the microprocessor PIC. A fork oscillator of 32.768 KHz can be used to prevent the battery  33  from being consumed. An oscillation circuit is formed with the capacitors C 12 , C 13 , etc. 
     When a voltage of +5 volts with an impedance of 240 KΩ is provided to the pad of W 3 , the operating mode of the microprocessor PIC is switched to the debug mode to confirm operation of the LCD  26  and internal circuits. (This is the test mode mentioned above). 
     When the pads of W 2  and W 4  are shorted, the total time that the lamp has been lit is shown by the lamp life meter  3  without being connected to the light source unit&#39;s main body  2 . 
     For reference, FIG. 10 shows the internal configuration of the preferred microprocessor PIC. Basically, it comprises PROM  61 , RAM  62 , I/O A 63 b, I/O A 3 b, resistors, timer  64 , oscillation unit, etc. 
     Since two 55 milliamps/hour, silver oxide cells are preferably used, the capacity is 110 milliamps/hour. Even when the batteries  33  are not used, however, their capacity will be reduced to 70% of the initial capacity due to natural discharge after five years. 
     In order to save power consumption, the following settings are preferably made for the microprocessor PIC: LP mode, on; watch dog timer, off; without input/output pull-up; power-supply voltage, 2.8 volts. Therefore, the power consumption is typically 26 μamps and maximum 53 μamps during the operation mode, and typically 0.7 μamps and maximum 2 μamps during the sleep mode. 
     The maximum power consumption of the LCD  26  is 1.3 μamps. 
     So constructed, the worst operable time can be estimated as follows. 
     During continuous operation: 110 milliamps/hour/(54.3 μamps×1 hour)=2025 hour&lt;1417 hour&gt;. 
     During the sleep mode: 1 μamps/(2 milliamps/hour×1 hour)=55500 hour&lt;38500 hour&gt;. 
     When 500 hour operation and the sleep mode: ((110 μamps−(500 μamps−(500 hour×59.3 milliamps/hour))/(2 milliamps/hour×1 hour)=41425 hour&lt;28998 hour&gt;. 
     N.B. A figure put in angle brackets is the operable time when the meter is first used after batteries  33  have been left unused for five years. 
     Since the worst happens rarely, the operable time is longer in most cases. 
     Actually measured value during operation: 20 milliamps/hour or less. 
     Actually measured value during sleep mode: 0.1 milliamps/hour or less. 
     An example of patterns displayed during the normal mode of operation are shown in FIG.  12 . 
     As shown in the timing chart of FIG. 11, the LCD  26  driven by microprocessor PIC displays various patterns by inverting the potential between the bar to be lit and the common line  32  times a second. In order to save the battery  33  as much as possible, bars blink (they flash on and off every second). The patterns displayed vary as a function of the time the lamp  11  has been lit. 
     An example of patterns displayed during the check mode is shown in FIG.  13 . 
     When a voltage of +5 volts with an impedance of 240 KΩ is provided to the DEBUG MODE pad, the mode is switched to the test mode, and patterns of the test mode are displayed. The test mode cannot be released unless power is shut off. 
     Next, the preferred algorithm of the internal program will be described. First, the main routine is shown in FIG.  14 . 
     When the power is provided by the battery  33 , the microprocessor PIC resets to start the program. When the program starts, an -initialization program runs to set the variable fields or constants as shown in Step S 1 . In Step  2 , the microprocessor PIC determines whether the main-lamp-on signal is present. In the case of the “L” level where the signal is not present, the microprocessor PIC switches to the sleep mode, as shown in Step S 3 , to minimize power consumption. 
     In Step S 4 , the microprocessor PIC determines whether there is an interrupt request. If not, the sleep mode is maintained. When there is an interrupt request, the program returns to Step S 2  to switch to the normal mode. 
     On the other hand, when the input signal is “H”, indicating the main-lamp-on signal is present, the microprocessor PIC determines whether the debug signal input in Step S 5 . When the input signal is “L”, where the debug signal is not input, the program returns to Step S 2 . When the input signal is “H”, it returns to Step S 2  after setting the check mode flag (DFLG) to 1 in Step S 6 . 
     Steps S 2  through S 6  are repeated. A timer interrupt arises every {fraction (1/32)} second, and the program branches to the interrupt routine. 
     Referring to FIG. 15, the timer interrupt routine will be described. When jumping to the timer interrupt routine, the register is copied to another area to be saved in Step S 11 . In Step S 12 , all interrupts are halted so that no other interrupt may arise while the timer interrupt is being handled. Next, the timer-counter is set in Step S 13  to allow a timer interrupt to be requested every {fraction (1/32)} of a second. Then, the timer interrupt procedure is started in Step S 14 . Next, the copied contents of the register are copied to the register in Step S 15  to recover the register. 
     Next, whether the normal mode or the test mode should be adopted is determined based on the contents of DFLG in step S 16 . If DFLG=0, the normal mode will be adopted; and if DFLG=1, the test mode will be adopted. 
     In the case of the normal mode, the display mode is set in Step S 17 : a display mode is selected from the following three based on the number of frames, the number of seconds, and the lapse of time, and a pattern is displayed by the LCD in Step S 18 : 
     i) Not displayed with bars (even second) 
     ii) Displayed with bars (odd second, odd frame) 
     iii) Displayed with bars (odd second, even frame) 
     Next, the total time is counted in Step S 19 . Then, the program returns to the main routine. 
     On the other hand, in the case of the test mode, the display mode is set in Step S 20 . A display mode is selected from the following based on the number of frames and the test procedure, and a pattern is displayed by the LCD in Step S 21 : 
     i) Not displayed with bars 
     ii) Displayed with bars (odd frame) 
     iii) Displayed with bars (even frame) 
     After calculating the display situation in Step S 22 , the program returns to the main routine. 
     A principle characteristics of the lamp life meter  3  according to the preferred embodiment is that it is similar in configuration and requirements to the traditional-type lamp life meter  81  detachably attached to a socket  6   a  that can place a minimal-ampere direct-current voltage between two terminals when lamp  11  is lit, wherein a display indicates the remaining life of the lamp as a function if the total time during which the lamp on direct-current voltage is placed between the two terminals of the socket. 
     Next, operation of the lamp life meter  3  will be described. 
     The lamp life meter  3  is attached to the lamp life meter socket  6   a . When the lamp life meter  3  is first used (in its factory-shipped configuration), an insulating tape  44  is located between the battery  33  and the electrode terminal  52   a  in the battery holder at a position where current flow between the battery  33  and the electrode terminal  52   a  is prevented. 
     When the user wants to use the lamp life meter  3  for the first time, the insulating tape  44  must be removed. When this is done, the lamp life meter  3  will be on stand-by. When an AC input is provided to the light source unit and a lamp lighting switch (not illustrated) located on the display panel  14  is turned on, a signal is output to the lamp lighting circuit  12  by the control unit  15  to light the lamp  11 . 
     When the lamp  11  is lit, a positive potential is provided to the input terminal  24  simultaneously with lighting of the lamp  11  because the lamp life meter  3  is attached to the socket  6   a . The input terminal  25  is at the ground potential. (Before positive potential is provided to the terminal  24 , the CPU  31  of the lamp life meter  3  is on the sleep mode (standby), and not in counting mode.) When a positive potential is provided to the input terminal  24 , the CPU  31  starts to operate for counting, and lights the LCD  26 . At the outset, the total elapsed time is 0 hours from which the conducting time will be counted. 
     In the present embodiment, the total time is displayed by the LCD  26  constituted of nine bars as shown in FIG.  3 . Up to a total time of 300 hours, the next right-hand bar is lit every 50 hours. From 300 hours to 500 hours, the next right-hand bar is lit every 100 hours. Above 500 hours, the highest-rank bar (at the far right) is lit. The bar of the LCD  26  for showing the total time blinks every second. Depending on the specifications of the instrument being used, continuous lighting or bar lighting may be selected. The bar pattern displayed by the LCD  26  may be replaced with a matrix display or 7-segment numerical display or any other suitable display. 
     When the light source unit&#39;s main body  2  finishes lighting the lamp  11 , the power provided to the lamp life meter socket  6   a  is shut off. When this signal is detected by the CPU  31 , the total time counted until that time is backed up by the memory (for example, the RAM  62  in FIG.  10 ), and the sleep (standby) mode is re-adopted. The data on the total elapsed time backed up by the RAM  62  is saved thanks to the battery  33 . 
     When the lamp  11  is lit again, the total conducting time is counted again based the value backed up the previous time, and the cumulative time can be counted without a break, and displayed. 
     In the operation test mode, bars of the LCD  26  can be lit one by one or all the bars can be lit at the same time to check whether there are bad cells or not. 
     The present embodiment has the following merits. 
     (a) Because it is possible to know how long the lamp life will last, an unexpected shut down or run down of the lamp during operation can be avoided. 
     (b) Because it is possible to know how long the lamp life will last, the endoscope system including a light source unit can always be used with a feeling of security. 
     (c) Because it is possible to provide a lamp life meter compatible with the traditional model, existing light source units can be continued to be produced without changing their specifications. 
     (d) Because means are provided to shut off the embedded power source before the lamp life meter is first used, the battery can be prevented from being consumed, and used for a longer time. 
     (e) Because an operation test means is arranged in the main body of the lamp life meter, a test operation can be easily performed during the manufacturing process, and production efficiency can be improved. 
     (f) Because an operation test means is arranged in the main body of the lamp life meter, a test operation can be easily performed during use, and secure services can be offered to the user. 
     In the above-mentioned embodiment, the lamp life is shown as a function of the total time for which the lamp  11  has been lit. Alternatively, it is possible to directly indicate how much battery time remains. This can be done by subtracting the total time for which the lamp  11  has been lit from the expected life of the lamp (500 hours, for example)and displacing the result. 
     It is also be possible to use the lamp life meter  3  with different lamp sources whose life expectancies differ. This can easily be done by sending information to the microprocessor indicating the expected life time of the particular lamp being used. 
     The embodiment described above is applied to an endoscope light source unit  1 . Since the essential function of the lamp life meter  3  is to count the time period that an operating signal (e.g. the lamp on signal) appears on the input terminals  24 ,  25 , however, it can also be applied to other fields. [For example, indication of the time when the toner of a copying machine should be replaced, life of VTR head, life of a projector lamp, etc.] 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but; only by the appended claims.