Cata-Dyne™ Infrared Oven

Operation and Instructional Manual - Voltmeter Tests

Voltmeter Tests

Ensure that the negative (black) lead of the meter is connected to signal common as described earlier (refer to drawings TC_MEAS1, 2, 3 or 4).

Begin by measuring the power supply voltage.  A voltage less than 12 VDC indicates a possible power supply problem.  A voltage near 0 usually indicates a short or other overload - confirm this by feeling (gently!) the gold colored discs near the edge of the CPU boards.  A disc that is too hot to touch indicates an overload.  Look for strands of wire touching where they should not be.  Record the measured power supply voltage, you will need this reading for some of the tests following.

Measure each connected heater’s signal lead.  A signal voltage reading of 0.75 VDC to 4.25 VDC on the signal terminal is normal.  Refer to the table at the end of this document to determine the heater temperature.

A signal voltage near 0 VDC indicates a disconnected or defective thermocouple pre-amp.  Measure the voltage across the two output terminals at the pre-amp card.  A voltage reading of 0 VDC indicates a broken or disconnected wire.  A voltage exactly equal to the measured power supply voltage indicates a defective pre-amp channel.  A voltage between 5 VDC and the measured power supply voltage is normal.

A signal voltage reading above 4.75 VDC is also an alarm condition.  If the signal voltage is exactly equal to the measured power supply voltage, look for a short on the two wires that connect that pre-amp channel to the CPU card.  Try disconnecting one of the wires for that channel at the pre-amp board and see if the signal voltage drops to 0.  If it does, the pre-amp is most likely defective.  If not, there is a short in the pre-amp wires back to the CPU.

A signal voltage reading that is a couple of volts less than the measured power supply voltage most often indicates a disconnected or defective thermocouple.  Try disconnecting the thermocouple from the pre-amp board and measuring its resistance.  A resistance greater than 25 ohms indicates a defective thermocouple.  Also try putting a jumper wire on the R-Y terminals of that pre-amp channel in place of the thermocouple.  The signal voltage at the CPU card should now read between 0.75 VDC and 1.0 VDC.

The last problem is best diagnosed when starting the oven from a cold start.  Measure the signal voltages on all the connected thermocouple channels every 20 seconds or so and observe the voltage change as the heaters warm up.  A channel that shows a voltage DECREASE as the heaters warm up indicates that the thermocouple is wired to the pre-amp card backwards.  If the wire colors match the letters on the card, replace the thermocouple in the heater.  On rare occasions, the thermocouple manufacturer has been known to swap the lead wires inside the epoxy transition area at the rear of the thermocouple.  This causes all manner of strange readings and can only really be detected from a cold start (while the back of the heater is at cold).  A thermocouple that has its lead wires reversed inside the transition is not usable and must be replaced.

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