Emerson Nelson CM-1, Manual

Page: 17 / 24

www.nelsonheaters.com
GA-2129 Rev. 11
Sheet 17 of 22
Jul. 2018
CURRENT ADJUSTMENT PROCEDURE
The CM-1 sensor card has an adjustable current alarm. The current adjust feature works with all types of
heater cables; self-regulating, constant wattage and MI. The sensor cards come from the factory preset to a
minimum current alarm level of 50 milliamps. Current flow above the minimum threshold is indicated by a
red L.E.D. located on the sensor card by each circuit.
1) Each circuit must be individually adjusted under operating load conditions. Circuits are sequential,
starting with circuit No. 1 on sensor card M1. There are four circuits per sensor card.
2) Apply power to first circuit to be calibrated. Be sure that the thermostat contacts are calling for heat.
This may require that you temporarily adjust the thermostat set-point higher to get the unit to close, if
you do,
BE SURE TO RETURN IT TO THE PROPER SET-POINT AFTER CALIBRATION.
3)
At this point the circuit to be calibrated should be indicating “HEATER ON” (green light ON). Some
heater cables have a higher inrush current when first turned on.
ALLOW HEATER TO OPERATE
NORMALLY FOR 24 HOURS BEFORE STARTING CALIBRATION OF CURRENT
ALARM.
4)
Locate the sensor card’s current trimpot for the circuit to be calibrated. The trimpot is a blue
13mm x 19mm (0.5” x 0.75”) device with a brass adjusting screw located about 25mm (1.0”) to the
left of the Load Terminal Strip. See Figure 17 for red L.E.D. and the adjustment trimpot located for
each.
5) Turn adjusting screw clockwise with an INSULATED SCREWDRIVER until the red L.E.D. dims.
With the L.E.D. turned off the circuit is in ALARM.
6) Turn adjusting screw counter clockwise until the red L.E.D. comes fully ON. The circuit is now out
of ALARM and calibrated for the existing voltage and temperature conditions.
N3
S4
N4
S3
S2
N2
N1
S1
L4
N4
L3
N3
L2
N2
L1
N1
LINE LOAD
TRIMPOT
RED L.E.D.
Figure 15