Process control equipment for use in adverse environments

Abstract: Programmable apparatus for monitoring an industrial installation, such as for measuring the depth of material in bins or silos, utilizes a computer having a hermetic­ ally sealed case (60), with an externally visible display (38) and necessary connections to the installation being monitored. The computer includes non-volatile random access memory (10) for the storage of operating parameters which is written to under control of a portable external programming unit (58) which can temporarily access the computer via an infrared or equivalent communications link (2, 4). The case (60) of the computer has provision (74) for temporary docking of the programming unit, which has a keypad (54) for the selection of calibration and diagnostic routines, and the entry of data or commands to be transmitted to the computer.

Description: This invention relates to process control equipment for use in adverse environments, and particularly although not exclusively to measuring depths of solids and liquids in containers and channels. In recent years, wide use has been made of microprocessor based process control units for supervising industrial operations. Examples of such operations are the monitoring of the depth of material in silos and bins, the depth of fluid in channels, and the rate of flow of materials on conveyor belts. Typically, such equipment incorporates inputs from one or more transducers, connections to alarm or recording devices, and an operator interface consisting of some form of visual read out and some form of data entry keyboard which can be utilized for entering data into the unit. Electronically, the unit comprises a microprocessor associated with read only and random access memory and suitable peripheral interfaces so as to form a dedicated computer. Such a unit most commonly operates under very adverse conditions in terms of the presence of dust, dirt, moisture and rough handling, and at the same time is also usually required to maintain calibration within fairly narrow limits. In this connection, the provisions for data entry in conventional units are a weak point, both since the keyboards are vulnerable to the adverse conditions mentioned above, and because they may provide a means for unauthorised or inadvertent reprogramming or recalibration of the unit. Whilst measures can be taken to alleviate these problems, they increase the cost and complexity of the unit and its programming. The present invention seeks to provide an improved unit for monitoring functions in an industrial installation, which is environmentally sealed, and requires no keyboards or other directly human accessible data entry device, whilst still permitting authorized amendment of the parameters of the monitoring function. EP-A-0180423 illustrates the use of a remote hand held infrared control unit to reset operating parameters within monitoring units. This disclosure relies upon two-way transmission between the control unit and the monitoring unit to provide an indication of the reset parameters at the control unit, the monitoring unit having no display of its own. What constitutes the present invention is set out in the following claim 1. The invention is described further with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of principal components of a level monitoring system incorporating the invention; Figure 2 is a schematic diagram of a calibrator unit for use with the system of Figure 1; Figure 3 is a flow diagram outlining the programming of the system of Figure 1; Figure 4 is a diagrammatic front view illustrating the interaction of the calibrator with a system unit; and Figure 5 is a fragmentary vertical section through part of the calibrator and system unit. Figure 1 is a simplified version of that forming Figure 1 of the United States Patent No. 4,596,144 (Panton and Woodward), with the difference that the keyboard 52 and control keys 58 of that patent are replaced by an infrared receiver 2 associated with an infrared sensor diode 4, and the division of the memory in three rather than two parts, read only memory 6, random access memory 8 and non-volatile memory 10. The non-volatile memory may be implemented by a conventional RAM with battery backup, or implemented by RAM chips with integral battery backup, or by electrically alterable and erasable read only memory, or magnetic bubble memory or any other suitable technology combining the ability to retain memory content under power down conditions with the ability to alter memory content under program control. The non-volatile memory, referred to for convenience as NOVRAM, is utilized for retaining constants which are dependent on a particular installation or configuration or which only require alteration at long intervals, such as configuration and calibration data. The read only memory 6 contains a predetermined program which controls a microprocessor 12, which in turn utilizes the random access memory 8 for working memory and temporary storage of variable data, whilst constants other than those predetermined by the program itself are stored in the NOVRAM 10. The main portion of the program itself, the relevant features of which are outlined in Figure 3, may be essentially as described in United States Patent No. 4,596,144 except for amendment to segregate the data addresses utilized appropriately between the memories 8 and 10, and any revision of the routines associated with an interface 14 to the receiver 2 so as to suit it to receive data from such a source rather than a keyboard or control keys. Further interfaces are provided to various other microprocessor peripherals. An interface 16 is provided to a transmitter 18 sending pulses to an external ultrasonic transducer 20, and interface 22 with an analog to digital converter 24 receiving return signals from the transducer 20 via a receiver 26, and from an external temperature sensor 28. The transducer 20 and sensor 28 are appropriately mounted in relation to a bin or silo 30 which is being monitored. An interface 32 is provided to an alarm relay unit 33, which may drive alarm indicator lamps 34 (see Figure 4) and possible external alarm devices, whilst an interface 36 drives a digital display 38. A further interface 40 drives a digital to analog converter and current source serial data transmitter 42. Whilst the various interfaces have been shown as separate functional blocks, it will be understood that they may be implemented by a lesser number of physical interface circuits providing multiple ports, or may be integrated either into the peripheral circuit which they interface or into a microcomputer which may incorporate the microprocessor 12 and all or part of the memories 6 and 8. The diode 4 associated with the receiver 2 can receive modulated data from infrared source diode 50 driven by a coding circuit 52, which causes the diode 50 to emit different pulse trains according to which key of a number of keys, typically about 20 on the keypad 54 has been depressed. The diode 50, encoder 52, a battery 56 powering the circuit 52, and the keypad 54, are incorporated into a small portable calibrator unit 58 (see Figure 4) which may be constructed similarly and utilizing similar devices, to the infrared remote control units widely used to control domestic appliances such as television sets. It should be understood however, as discussed further below, that the unit is not utilized as a remote control unit in the usual sense. The receiver 2 and diode 4 may also be similar to those utilized in remote control receivers and providing digital outputs responsive to key presses applied to a keypad on a transmitter. Referring to Figures 4 and 5, the components of the computer described with reference to Figure 1, apart from those described as "external" such as the transducer 20, the sensor 28, any external alarms, and the destination of a current source output from the block 42, are housed within a case 60 together with a suitable power supply (not shown). Typically the case 60 is of die cast construction with a die cast front cover 62 secured to the casing by screws 64 and sealed to it by an O-ring 66. The material from which the case is cast may be polycarbonate resin, which in the case of the front cover may be transparent, with an aluminum mask 68 attached to its inner surface, so as to leave a transparent window 39 for the display 38, and windows for the indicator lamps 34 and the diode 4, and to provide a protected surface for carrying user information such as a list 70 of operation parameters which can be altered, and a diagram 72 explaining some of those parameters. The front cover is moulded with a rectangular recess 74 which provides a docking bay for the unit 58. The unit 58 has a steel case, or at least a steel back plate 59 so that it may be releasably detained in the docking bay by magnetic strips 76. The sensor diode 4 is mounted behind the recess at a window in the mask 68, and the source diode 50 is mounted in front of a window 57 in the back plate 59 so that it is aligned with the diode 4 when the unit 58 is docked in the recess 74, thus establishing an optical path between the diodes. Operation of the microprocessor 12 is controlled by a program stored in ROM 6, a simplified flow diagram of this program being shown in Figure 3. The program consists of a main program loop 82 through a main program 80, which represents the normal monitoring functions of the unit. In the example shown, this comprises: (1) sending an instruction through the interface 16 to the transmitter 18 to apply a pulse to the transducer 20, and storing to RAM 8 the return signals picked up by the transducer 20, processed by the receiver 26 and digitized by the analog to digital converter 24; (2) analyzing the profile to obtain and store in RAM 8 data representing the elapsed time from transmission of the pulse to receipt of a line echo, using for example one of the techniques set forth in United States Patent No. 4,596,144. (3) calculating data representing the level of material in the silo 30 based upon the elapsed time data and data stored in NOVRAM 10; (4) displaying the level data on the display 38, as well as triggering appropriate alarm relay 34 in the event that the data is abnormal; and looping back to step (1). It will be understood that the above loop has been outlined merely for the sake of example, and could be replaced by any of the methods disclosed in United States Patent No. 4,596,144, or other alternative methods capable of being controlled by a repeatedly executed program loop, or by other such techniques appropriate to some other equipment being monitored. The loop may contain subsidiary loops. For example, if the equipment being monitored was a belt scale, the program might include an inner loop involving receipt of a trigger pulse from a tachometer generator, sensing and digitizing the output of load cells associated with the scale, and an outer loop integrating the digitized output signals and calculating, on the basis of constants stored in NOVRAM, the flow rate and/or total weight of material being conveyed. Moreover, this main program loop may include alternative subroutines which are selected on the basis of data stored in the NOVRAM 10, for example to carry out different alternative processing algorithms on the basis of the data captured, or to selected different data to display or different forms of data. The actual content of the main program loop may be varied to suit the application provided that the loop includes some safe point of exit and re-entry from the routines described below. Under normal operating circumstances, the program will follow the main loop and provide a display as determined by the constants stored in NOVRAM 10, until caused to exit the loop at 84 by receipt by the interface 14 of a signal indicating that data is being received by the diode 4. Conveniently this is achieved by programming the interface 14, upon power up of the computer in an initiation step 86 and prior to entering the main program loop 82, to issue an interrupt to the microprocessor 12 in response to receipt of data from the receiver 2, causing the latter to enter an interrupt service routine. Alternatively, the main program 80 may include a polling routine which periodically tests the interface 14 to determine whether it holds data and branch to an equivalent of the interrupt service routine. The service routine tests the data received to determine whether it is a valid signal to leave the main loop, and if it is so, causes execution to branch from a suitable exit point 84 to a secondary program loop 88. A suitable exit point will normally be on completion of a circuit of the main loop at 82, and if this is likely to take appreciable time, the service routine may cause a message or acknowledgement to be displayed on display 38 pending completion of the loop. For example, the message may be CAL to indicate entry to a calibration mode, which message can be displayed using characters that can be displayed by a conventional seven-segment digital display. A valid signal to leave the main loop will typically be that received by receiver 2 in response to pressing of a particular key on the keypad 54 when the unit 58 is docked in the recess 74. In the example shown this key is selected to be RUN/CAL (run or calibrate) key 55. Upon entering the secondary program loop 88, the next step 85 is to wait for data representing a further keystroke. On receipt of such data, a test is made at 90 to determine whether it represents the RUN/CAL key 55 or some other key. In the event that the RUN/CAL key has been pressed execution branches at 90 back to the re-entry point of the main program loop 82. The RUN/CAL key is thus utilized to toggle execution between the main and secondary program loops. Different keys or keystroke sequences could be utilized to achieve this toggling, but the technique described is simple both to use and to implement. In the event that the next keystroke data received does not represent the RUN/CAL key 55, then execution loops through a secondary program 92 and back to step 85. Typically, a primary function of the secondary program 92 is to examine and alter parameters in the form of constants which are stored in the NOVRAM 10 and utilized by the main program 80. In the example being considered, the secondary program operates to process successive key presses entered through the keypad 54 so as to result in codes being transmitted to the interface 14. Assuming that it has been decided in step 90 that the codes do not represent the RUN/CAL key, the code received is compared with successive codes to determine whether it is a function key, and if so which one, or a numeric key, and the program branches to different subroutines accordingly. The NOVRAM 10 is organized to provide storage for data representing a number of predeterminable parameters of the equipment being monitored, for example the dimensions of a silo being monitored, and high and low alarm levels, the manner in which data is to be presented, for example in metric or other units, whether various options are present or enabled, and whether or not to display values determined or determinable from values determined by the main program, but not normally displayed. Each such data item is allocated a parameter number which identifies the address in the NOVRAM of the data item concerned. Parameter numbers may also be utilized to identify certain test, diagnostic and calibration routines which it may be desired to select by means of the keypad, as described further below. The secondary program presents two alternative classes of data to the display 38, firstly parameter numbers which are identified by the prefix P, and secondly data associated with those parameter numbers, and the program itself operates in two phases according to whether parameters are being selected or data displayed. In general, the program is toggled between these phases by detection of successive presses of the ALT DISP key 94. In the parameter selection phase, a parameter number is selected and displayed by selective use of the *, ↑, ↓ and numeric keys. Thus the * key for example causes selection of parameter 01 and display of the characters P-01, the ↑ and ↓ respectively increment or decrement the parameter number stored and displayed, and entry of a 2 digit (in this example) number causes selection and display of the corresponding parameter number if available. Once a desired parameter number has been selected, a press of the ALT DISP key 94 will cause the program to enter its second phase in which a routine is selected according to the parameter number selected. If the parameter number designates a constant held in NOVRAM, then a routine is called to display the value of that constant. When a constant is so displayed, detection of a press of the ↑ or ↓ key will result in execution being temporarily returned to the first phase of the program for selection and display of an incremented or decremented parameter number, followed by a return to display the data associated with the newly selected parameter. Detection of presses of numeric keys during display of a numeric constant will result in replacement of the displayed constant by the numerals keyed in, whereafter the keyed in value may either be cleared using the CLEAR key or entered using the ENTER key, in which case it will be stored in NOVRAM in replacement of the previously stored value. It will be understood that by use of the keys in the manner outlined above, the parameters stored in NOVRAM 10 may be quickly and easily reviewed and modified. These parameters may include not merely numeric data concerning dimensions of apparatus being monitored, alarm thresholds and similar data, but may include data which is tested by the main program for example to determine which of several different data processing algorithms are to be utilized, or what class of data is to be displayed by the main program and in what form. As mentioned above, some parameters do not identify data stored in NOVRAM, but instead are utilized to initiate test of diagnostic routines. For example, selection of a particular parameter may be arranged so that a press of the ENTER key calls a routine which pulses all of the segments of the display and the alarm relays on and off so as to verify their function. Selected parameters may be utilized to access routines useful during set up and calibration. For example, U. S. Patent No. 4,596,144 describes methods of detecting a true echo in an ultrasonic range finding system which are essentially of a statistical nature, and not only identify an echo resulting from a particular shot but are capable of quantifying the degree of assurance that a selected echo is a true echo. This latter information may be utilized in determining whether additional shots are required to provide reliable data. We have now determined however that this assurance factor can be very advantageously utilized to facilitate installation of ultrasonic range finding transducers. The siting of such transducers in an installation to be monitored has hitherto called for considerable skill and experience combined with trial and error testing if good results are to be obtained. We have found that by entering a selected parameter to call a routine in the secondary program which calls a routine in the main program, to cause the transmitter to fire a single pulse and processing of the received signal to select the true echo and obtain the assurance factor that this is the correct echo, and which then displays the assurance factor, then by repeated entering of the parameter as the transducer is positioned, the latter may be located in the position which provides the highest assurance factor and thus the best chance of selecting the correct echo. It should be noted that this position will not necessarily be the position producing the strongest echo or highest transducer efficiency, since the strength of the true echo is less important than the ability of the signal processing circuit to isolate it from spurious echoes, which it may be possible to minimize by careful positioning of the transducers.

Claims: A unit providing a predetermined monitoring function for an industrial installation comprising an environmentally sealed casing (60) containing a computer comprising a microprocessor (12), a read only memory (6) accessible by the microprocessor and containing a stored program dedicating the microprocessor to the monitoring function, window means (39) in the casing, a first peripheral interface element (16) interfacing the microprocessor (12) to connections for a monitoring transducer (20) external of the casing and associated with said installation, a first random access memory (8) accessible to the microprocessor (12) and providing working memory and temporary data storage therefor, a radiation transducer (4) within the casing and responsive to data modulated radiation of the type to which a part of the casing is transparent, a second peripheral interface element (14) interfacing the microprocessor to said radiation transducer (4), and a second random access memory (10) which is non-volatile, accessible to the microprocessor (12) and provides storage for data relating to normally constant parameters of said monitoring function, a portable keypad unit (58) which comprises a keypad (54) having plural keys and means including a radiation source (50) to generate data modulated radiation according to which of said plural keys is depressed, characterised in that the casing (60) includes a dock (74) to receive a part of said keypad unit (58) such as to locate said radiation source (50) in alignment with said radiation transducer (4), and in that a human readable visual data display device (38) is provided within the casing, with a third peripheral interface element (36) interfacing the microprocessor (12) to said data display device (38), said display device being visible through said window means (39), and in that said stored program consists of a first normally active portion (80) configuring the computer to carry out the at least one monitoring function of the unit, said portion accessing said second memory (10) only for the reading of said normally constant parameters from defined locations therein, and a second normally inactive portion (92) operative to decode signals received from the radiation transducer (4) by the second peripheral interface element (14) to recover data representing said normally constant parameters, and to store said data in said defined locations in said second memory (10) responsive to said signals, the second peripheral interface element (14) including means (90) responsive to receipt of signals from the radiation transducer to activate said second program portion. A unit according to claim 1, characterized in that the dock (74) is a recess in a transparent lid (62) of the casing (60), said recess being shaped to receive a rear casing (59) of the keypad unit (58) opposite the keypad (54), the radiation source (50) is adjacent a window (57) in said rear casing, and the radiation transducer (4) is mounted within the casing (60) behind the recess (74). A unit according to claim 2, characterized in that the rear casing (59) of the keypad unit (58) comprises ferromagnetic material, and magnets (76) are secured within the recess (74) to detain the keypad unit (58) therein. A unit according to any of Claims 1 to 3, characterized in that the means (90) responsive to receipt of signals from the radiation transducer (4) is responsive only to a signal representing a specific key, and the second program portion (92) includes a routine responsive to a signal representing a specific key to de-activate said second program portion (92) and re-activate said first program portion (80). A unit according to any of Claims 1 to 4, characterized in that the monitoring transducer (20) is a sonic transducer of an acoustic ranging system which transmits pulses of sound energy and receives reflected energy in the form of echoes from a surface whose distance is to be determined, wherein the first program portion (80) executes a program loop which contains a shot routine which causes the transmission of a pulse, the reception of reflected energy, the identification of echoes, and the calculation of echo parameters, and wherein the second program portion (92) sets the parameters utilized by the first program portion (80) in performing its functions. A unit according to Claim 5, characterized in that the second program portion (92) includes a test routine selectable by signals from the keypad (54) which returns to the first program portion (80) for a single execution of the shot routine and then returns to the second program portion to display an echo parameter, and wherein one of the echo parameters determined by the shot routine is indicative of the degree of confidence that the correct echo has been determined and it is this parameter that is displayed, whereby by repeated selection of the test routine the effect of adjustments of the transducer (20) may be assessed.

Inventors: WOODWARD STEVEN J, WOODWARD, STEVEN J.
Applicants: FEDERAL IND IND GROUP INC, MILLTRONICS LTD.
Application year: 1987
Main classification: G01S15
IPC codes: G01S7, G01S15, G01F23