Watlow MLS - Manual (Page 124)

112 MLS User’s Guide
Troubleshooting
• To check thermocouple inputs, unplug the AIM module and measure
between the A+ and A- terminals of the AIM-TB. Thermocouple
inputs should not read above 200 ohms.
• To check RTD inputs, unplug the AIM module and measure between
the A+ and A- terminals. Then measure between the A+ and A
COM terminals of the AIM-TB. RTD inputs should read between
20 and 250 ohms. Both readings should be the same.
Make sure other inputs operate within the AIM's full scale voltage (60
mVdc). If they do not, install scaling resistors on the MLS-AIM-TB (see
Chapter 2: Installation).
Checking PID Control Outputs
To check control outputs:
• Set the loop you want to check to Manual mode.
• Set the output power percentage to the desired level.
• Set the output type to On/Off or TP (see Chapter 4: Setup).
Testing Control Output Devices
To test a control output device like an SSR, use a digital multimeter set
to DC voltage. Connect the positive lead of the multimeter to the MLS
+5V and the negative lead to the control output. The multimeter should
read 0 Vdc when the output is 0% and +5 Vdc when the output is 100%.
If the control output is not connected to an output device like an SSR,
connect an LED in series with a 1K resistor from +5 V to the output.
(Tie the anode of the LED to +5V.) The LED should be Off when the
output is 0% and On when the output is 100%.
Checking Digital I/O
You can check digital inputs and outputs from the Setup menus (see
Chapter 4: Setup) or you can use the techniques described above for
PID control outputs.