1977/06/29 Caterpillar

Special Instruction Form GMG00697-02, "Using the 1P3060 Pyrometer Group", gives information needed to test, do regular maintenance and make some repairs on this tool group.

The FT1012 and FT1013 Calibrated Circuits shown on Page 9 of this Special Instruction are not correct and must not be used. These tools were to be used to check the reading accuracy of the pyrometer.

A new procedure must be used for this purpose. An explanation of this procedure will be part of a new special instruction which will soon be available. The new procedure permits the pyrometer scale to be checked at 800°F, 1200°F and 1600°F. To do this, a controlled voltage is sent to the pyrometer across a 3 to 4 ohm resistance over a new calibration circuit. Example calibration points, input voltage and temperature, are shown in a chart. If at any one of these points the pyrometer reading error is more than ± 16°F, the unit must be sent to Alnor Instrument Co. for repair. The address shown in Special Instruction Form GMG00697-02 is wrong. Send the pyrometer units to:

If you do not have the equipment to check pyrometer accuracy, most electronic repair shops can normally make these checks in less than half an hour.

New calibrator circuit.

New Calibration Procedure to Check Reading Accuracy of the 1P3060 Pyrometer Group

Only use the calibration circuit and information that follows to check the pyrometer reading accuracy:

Circuit Conditions

1. All resistors are 1/4 watt, 20%.

2. Digital voltmeter (DVM) has a maximum resolution of 100 microvolts (10 microvolts minimum) and not less than 0.1% accuracy.

3. 12 VDC can be a 12 volt automotive battery or a bench power supply.

4. R1 is a carbon potentiometer (volume control).

NOTE: The circuit does not have to be exact, but the voltage produced (made) across the resistance must be known.

The input power (12 VDC) is decreased to millivolts when sent across the three parallel resistors. This is similar to a thermocouple output with 3.33 ohms resistance. The potentiometer (R1) is adjusted until the digital voltmeter (DVM) reads each of the values in the chart that follows. The pyrometer must read the temperature opposite, within ± 16°F.

NOTE: If a bench power supply is used, the potentiometer (R1) can be zero ohms and the power supply voltage can be adjusted to give the necessary calibration voltages.