HAND-HELD THERMOCOUPLE THERMOMETER SERVICE MANUAL. CATALOG NUMBERS , and , and PROPRIETARY

Transcription

1 HAND-HELD THERMOCOUPLE THERMOMETER SERVICE MANUAL CATALOG NUMBERS , and , and PROPRIETARY Information contained in this manual is proprietary to COLE-PARMER INSTRUMENT CO., INC. No reproduction for other than the intended use of maintaining the product described herein is permitted without the written permission of COLE-PARMER INSTRUMENT CO. Cole-Parmer Instrument Co. 625 East Bunker Court Vernon Hills, IL USA (847) (800) A Edition 03 9:07 AM 4/5/2004 Page 1 of 14 A

2 TABLE OF CONTENTS SECTION I SECTION II SECTION III SECTION IV FUNCTIONAL DESCRIPTION BLOCK DIAGRAM CIRCUIT DESCRIPTION SCHEMATIC DIAGRAM REPLACEMENT PARTS LIST TROUBLESHOOTING CALIBRATION PROCEDURE FUNCTIONAL CHECK 9:07 AM 4/5/2004 Page 2 of 14 A

3 FUNCTIONAL DESCRIPTION This Hand-Held Thermocouple Thermometer is a microprocessor-based, precision instrument, for use with any one of J, K or T type thermocouples. The unit features a large, 0.5-inch high liquid crystal display with annunciators, a four button silicon rubber touch keypad, a splashproof plastic case, and is intrinsically safe. Factory calibration is maintained in a non-volatile memory (EEPROM). Readings may be displayed in Fahrenheit or Celsius. A reading Hold function and field calibration for probe offset is also included. BLOCK DIAGRAM 9:07 AM 4/5/2004 Page 3 of 14 A

4 CIRCUIT DESCRIPTION Please refer to the schematic diagram (page 9) while reading this circuit description. Power Supply The power supply circuits perform multiple functions: convert the battery to a steady +3.3V, switch the meter on and off, and provide a reset to the microprocessor. Power to the meter is supplied by two 1.5-volt Alkaline AA batteries. R1 provides intrinsic safety current limiting. U1 and its associated circuitry comprise the power supply. This is configured as a step-up switching regulator with a +3.3 V output, and a 1.0 to 3.2 volt input. The +3.3 is applied to Q1, which acts as an electronic On/Off switch. With the shutdown ( SHDN ) pin connected to the output of this switch, whenever the switch is off, U1 enters a standby mode in which it consumes less than 1 microamp of current. To activate this circuit, the On/Off switch is pressed, which grounds one end of R6. This turns on Q1 which in turn brings the shutdown pin of U1 high, thus starting the regulator. With the +3.3 now up, and the On/Off switch still held down, the latch formed with U5B and U5C, latches Q2 on. Once this happens, you may then release the On/Off switch and the meter will stay on. The output of Q1 has a slow rise time, typically 100 milliseconds. This is too slow for the microprocessor to reset. Since the low battery input pin ( LBI ) of U1 is a precision comparator, it is used to sense when the power supply output has risen to greater than +2.5 volts. At this point the low battery output pin ( LBO ) goes high, which allows C5 to charge, and complete the microprocessor reset sequence. To switch the power supply off, the microprocessor first senses that you have again pressed the On/Off switch. It then blanks the display and waits for you to release the On/Off switch, at which time it clears port pin R40, which causes the U5 latch to toggle, thus turning off Q2, and in turn, Q1. Analog Circuitry The analog circuits consist of a bias and filter network for the thermocouple, an ambient sensor circuit with linearization, an eight channel multiplexer, a 1.25-volt voltage reference, and a discrete single slope analog to digital converter (A/D). Since all voltages within this meter must be positive, and since a thermocouple may produce a negative output voltage differential, a bias network 9:07 AM 4/5/2004 Page 4 of 14 A

5 is used to keep all thermocouple voltages positive. This is R20 and R23. Low frequency filtering is provided by C10, C11 and C12, while high frequencies are attenuated with L3 and L4. The two sides of the thermocouple are connected to two inputs of the multiplexer. Other inputs to the multiplexer are the reference voltage, the ambient sensor, a battery voltage sense and an offset voltage for the A/D converter process. Analog to Digital Converter (A/D) This A/D converter provides 16 bits of resolution ( 1 part in 65,535 ), with a conversion time of 50 milliseconds. It consists of a DC amplifier, window comparator, analog integrator, gated clock and the microprocessor. The output of the multiplexer is applied to a DC amplifier, U3A, which has a fixed gain of 14. This is connected to the upper side of a window detector, U4B. U3B forms an analog integrator. Its output is connected to the lower side of a window detector, U4A. Figure 1 shows a typical A/D conversion cycle. Vin is the output level at U3A, and has a normal range from 500 mv minimum to 2 V maximum. VL is the voltage present at U4A-2, typically 450 mv. TPA goes low to signify the start of the measuring period, while TPB goes low to signify the end of the measuring period. The microprocessor counts the clock pulses, at the output of U5D, while the gate is high, but only between T3 and T4. Beginning at T0, the emitter of Q3 is raised high. This allows the output of the integrator, U3B, to rise. At T2, when the integrator output crosses the input level, Vin, the microprocessor pulls Q3 emitter low. The delay from T2 until this occurs is the small overshoot. As the integrator again crosses the Vin level, at T3, the gate again opens and the microprocessor begins counting clock pulses. This continues until T4, the point where the integrator crosses VL. With the gate closed, the microprocessor reads the number of clock pulses and converts this to a voltage, which is then used for calculating the thermocouple or ambient temperature or battery voltage. One of these conversions occurs for each multiplexer input. The multiplexer is switched from one channel to the next at time T4. The total time from T0 to T4 is a maximum of 50 ms. There is a 50 ms delay between conversions (from T4 to the next T0). This delay allows for the DC amplifier to settle. 9:07 AM 4/5/2004 Page 5 of 14 A

6 Figure 1. A/D Timing Other Features Thermocouple voltages are measured by taking readings of each thermocouple lead, with respect to ground, and subtracting the two values with the microprocessor. Calibration information and thermocouple type are stored in the EEPROM. Thermocouple type is determined when the unit is calibrated on the test fixture, which makes connection through the calibration access port. Alternately, there is a secret key combination that allows this to be changed: Note: Begin with power off. Press and hold the C/ F and HOLD buttons and then press On/Off. Wait about 5 seconds until the display shows a single digit number, 0, 1 or 2. Release the C/ F and HOLD buttons. A 0 represents K, 1 represents J, and 2 represents T. Use the C/ F button to select 0, 1 or 2, as required. Press the HOLD button. The selected thermocouple type is now stored in EEPROM. If different, the front panel label should be changed to match this new type. 9:07 AM 4/5/2004 Page 6 of 14 A

7 The liquid crystal display is of the static drive type. This means that the drive voltage is a simple square wave, with levels of 0 and +3V. The result is a very wide viewing angle (as compared to a multiplexed LCD). The microprocessor runs at 2.09 MHZ; this frequency should only be measured at U8-2. 9:07 AM 4/5/2004 Page 7 of 14 A

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9 REPLACEMENT PARTS LIST Barnant P/N Cole-Parmer P/N Description E-2105 E-2105 PCB Assy E-2525 E-2525 Input Connector Assy B B Screw, #2-56 B B Lockwasher, #2 E-2073 E-2073 Case, Front B-3556 B-3553 Overlay, Window B-3564 B-3558 Overlay, J B-3566 B-3560 Overlay, K B-3565 B-3559 Overlay, T D-2828 D-2828 Lens D-2818 D-2818 LCD B-3574 B-3574 Zebra Strip E-2075 E-2075 Keypad B B Case, Back B B Wire Bail D D Battery Clips E-2076 E-2076 Battery Door B B Fiber Washer B B Screw, Battery Door A-4498 A-4498 Foot, Bottom A-4497 A-4497 Pad, Bottom B B Screw, Case 9:07 AM 4/5/2004 Page 9 of 14 A

10 SECTION III TROUBLESHOOTING The following is a list of typical problems that might occur and possible remedies. Does Not Turn On Dead batteries -- replace with new ones. Bad battery connections -- check the clips for spring tension to the PC board. Batteries installed backwards. On/Off switch not working -- clean switch contacts. Low Battery graphic is on. Dead batteries If the batteries are OK, then the EEPROM may have lost calibration information. Error Messages Err -- field cal outside of 0±10 C (32±18 F) Err1 -- EEPROM has lost factory cal info -- recalibrate. Err2 -- EEPROM has lost stored thermocouple type or bad field cal data -- recalibrate. Err3 -- EEPROM write verify error -- replace EEPROM. Err4 -- A/D not running correctly, signal at TPA is wrong. Note: Thermocouple channels display Open for this condition. Err5 -- A/D not running correctly, signal at TPB is wrong. Note: Thermocouple channels display Open for this condition. Err6 -- A/D overflow (overranged). Note: Thermocouple channels display instead of Err6 to indicate over probe limit -- probably wrong thermocouple type. Err7 -- Bad 1.2V reference value stored in EEPROM -- recalibrate. Note: This error is not displayed if Err1 also exists. 9:07 AM 4/5/2004 Page 10 of 14 A

11 SECTION IV CALIBRATION PROCEDURE Basic Factory Calibration, Without The Aid Of A Test Fixture. 1. Determine software version. Install batteries. Begin with power off. Press and hold the C/ F button and then press and release On/Off. At the end of the display test, a software version will be displayed in the form x.x. For 1.0 proceed to step 2. For 1.1 and higher, proceed to step Perform this first step only if Err7 is displayed or if D4 has been replaced. Otherwise, you may proceed directly to step 4. This step requires that the UUT have power but you must also have access to the electronics at the top of the UUT. One suggested method is to take a rear case and cut off the top. Then install batteries into the bottom and attach the rear case with screws. Press On/Off to activate UUT; ignore the display. Measure the voltage at pin 8 (referenced to pin 4) of D4, the 1.2-volt reference, and write it down. You need four significant digits right of the decimal point, as in Attach the rear case normally, with batteries installed. 4. Begin with power off. Press and hold the CAL and HOLD buttons and then press and release On/Off. Wait until the display blanks, then release only the HOLD button--continue pressing CAL. Wait for CAL to begin flashing. Press and hold C/ F and release CAL. In a few seconds, the display will show 2300 (assuming this unit has not been previously calibrated) or, from the above example in step 2, would show Release C/ F. Now use C/ F and HOLD to increment/decrement the display to match the 4 significant digits determined in step 2. Press CAL. Proceed to step Begin with power off. Press and hold the CAL and HOLD buttons and then press On/Off. Wait until the display blanks, then release only the HOLD button--continue pressing CAL. Wait for CAL to begin flashing. Release CAL. 6. Using only K type thermocouple connectors and wire, and with the calibration source set for K type, apply +950 C or F to the UUT. (This K selection is true even if this is a J or T type unit.) Wait for the reading to settle and press CAL. The display will show 1 for a few seconds, then the display returns. 7. Apply 0 C or +32 F to the UUT. Wait for the reading to settle and press CAL. The display will show 2 for a few seconds, then the display returns. 9:07 AM 4/5/2004 Page 11 of 14 A

12 8. Connect a copper short to the input. Wait for the reading to settle and press CAL. The display will show 3 for a few seconds, then the display returns. 9. Apply 0 C or +32 F to the UUT. Wait for the reading to settle and press CAL. The CAL indicator should go off, and the UUT should indicate 0 C/+32 F, if the unit is selected as a K type. Calibration of software version 1.0 is now complete Begin here for software version 1.1 and higher; go back to step 2 for 11. Perform this first step only if Err7 is displayed or if D4 has been replaced. Otherwise, you may proceed directly to step 14. This step requires that the UUT have power but you must also have access to the electronics at the top of the UUT. One suggested method is to take a rear case and cut off the top. Then install batteries into the bottom and attach the rear case with screws. Press On/Off to activate UUT; ignore the display. Measure the voltage at pin 8 (referenced to pin 4) of D4, the 1.2-volt reference, and write it down. You need four significant digits right of the decimal point, as in Attach the rear case normally, with batteries installed. 13. Begin with power off. Press and hold the CAL and HOLD buttons and then press and release On/Off. Wait until the display blanks, then release only the HOLD button--continue pressing CAL. Wait for CAL to begin flashing. Press and hold C/ F and release CAL. In a few seconds, the display will show 2300 (assuming this unit has not been previously calibrated) or, from the above example in step 11, would show Release C/ F. Now use C/ F and HOLD to increment/decrement the display to match the 4 significant digits determined in step 11. Press CAL. Proceed to step Begin with power off. Press and hold the CAL and HOLD buttons and then press On/Off. Wait until the display blanks, then release only the HOLD button--continue pressing CAL. Wait for CAL to begin flashing. Release CAL. 15. Using only K type thermocouple connectors and wire, and with the calibration source set for K type, apply +950 C or F to the UUT. (This K selection is true even if this is a J or T type unit.) Wait for the reading to settle and press CAL. The display will show 1 for a few seconds, then the display returns. 9:07 AM 4/5/2004 Page 12 of 14 A

13 16. Apply 0 C or +32 F to the UUT. Wait for the reading to settle and press CAL. The display will show 2 for a few seconds, then the display returns. 17. Apply 0 C or +32 F to the UUT. Wait for the reading to settle and press CAL. The CAL indicator should go off, and the UUT should indicate 0 C/+32 F, if the unit is selected as a K type. Calibration of software version 1.1 and higher is now complete. FUNCTIONAL CHECK 1. Press and hold ON/OFF. Verify all LCD segments and characters as being present. This display should remain on as long as ON/OFF is being held down. 2. Release ON/OFF. If any Err # is displayed, tag the unit with the Err # and set aside. NOTE: The tolerances given in these steps do not allow for any error(s) originating from the calibration source. 3. Apply +0.0 C. Use C/ F key to select C. Verify the reading to be -0.5 to +0.5 C. 4. Use C/ F key to select F. Verify the reading to be to F. 5. Press HOLD. The HOLD designator on the LCD should be on. 6. Apply the following input value: J type C K type C T type +400 C 9:07 AM 4/5/2004 Page 13 of 14 A

14 The reading shall not change from above. 7. Press HOLD. The HOLD designator on the LCD should go off. 8. Use C/ F to select C. Verify the reading to be: J type +997 to C K type to C T type +398 to +402 C 9. Remove the thermocouple probe from the top of the UUT. The readings should begin decreasing (reading more negative), until the word OPEN is displayed. 10. Press and hold CAL for about 5 seconds until CAL blinks on the display. Release CAL. 11. Press ON/OFF to turn the UUT off. Test complete. 9:07 AM 4/5/2004 Page 14 of 14 A