Watlow MLS - Manual (Page 49)

Installation
MLS User’s Guide 37
• The A COM (AUX) terminal is the Auxiliary input. This is analog
common used for RTD inputs.
WARNING
Do not exceed 10 Vdc between loops. Excess volt-
age may damage the Analog Input Module (AIM).
Input Wiring Recommendations
Use multicolored stranded shielded cable for analog inputs. Watlow-
Anafaze recommends that you use #20 AWG wire. (If the sensor
manufacturer requires it, you can also use #22 or #24 AWG wiring.)
Most inputs use a shielded twisted pair; some require a 3-wire input.
Input Scaling
You can connect thermocouples, 4-20 mA current inputs, voltage inputs,
and 2- or 3- wire RTD inputs to the MLS. If you need to scale input
voltages or convert milliamp inputs to match the -10 to 60 mV (-16.7%
to 100%) input range, install scaling resistors. Watlow-Anafaze can
supply factory-installed input scaling resistors--order option MLS-SI-
XX (See the next table for standard scaling resistor values), or special
input kits MLS-SIK-XX (call Watlow-Anafaze for XX number).
Scaling Values
• Scaling values for mVdc ranges are standard metal film values with
+0.25% accuracy if 0.1% tolerance resistors are used.
• Scaling values for mAdc ranges are 0.1% tolerance with +0.10%
accuracy.
• Scaling values for RTD ranges are 0.05% tolerance. Use these values
to remain within factory specifications for the RTD inputs.
• Use 0.1% metal film, 1/4 watt resistors. Higher tolerances may cause
significant errors. Use the MLS' built-in linear scaling to correct
any errors due to resistor tolerance. You can also install other com-
ponents (like capacitors) for signal conditioning; please consult
Watlow-Anafaze for more information.
This figure shows an input circuit. RA, RB, RC, and RD refer to the
scaling resistor locations printed on the MLS-AIM's terminal board.