©201
7
Nelson Heat Tracing Systems
www.nelsonheaters.com
GA2497 Rev.
5
Troubleshooting
CM-2201/CM-2202
Note:
Ensure you refer to the correct RTD table for the
type
of
RTD you are using.
2. Temperature Verification ( Continued)
To verify the Controller:
TURN THE POWER TO THE CONTROLLER OFF BEFORE
PROCEEDING!
a) Disconnect the RTD wiring from the input terminals.
b) Connect
a 100 Ω
resistor
across
the
source
or
sense
terminal and common. Insert a jumper
between the
source and sense terminals.
c) Apply
power
to
the
controller.The
indicated
or
displayed
temperature should be about 3
2°F (0°C)
depending on
the actual resistance of the test resistor
if RTD TYPE
is
set to
100
Ω Platinum. Any resistor
may have a +/- 10% tolerance.
3. Unstable Temperature
An erratic indication of temperature can be caused by
several factors external to the controller. The controller’s
accuracy and resolution will result in an indicated
temperature change of a couple of degrees if the measured
resistance
temperature
falls
between
two
discrete
values (this
is
sometimes referred to as quantization
error).
If the instability is excessive, check:
a) Wire
used
for
extension
of
the RTD
should
be
three-wire,
twisted and shielded with the shield grounded at the
controller only. Each of the three lead wires must be of
the same gauge.
b) The ideal installation has a separate conduit for the
RTD
leads (if they have been extended).It is not usually
a
problem to run low signal levels in the same conduit
as
the power leads even in high power applications, as
long
as the RTD wire is a twisted, shielded type with an
insulation rating equal to or greater than the highest
voltage
in
the
conduit.
Follow
the
proper
Electrical
Code
requirements for your particular installation.
c) Check
the specifications for the particular cable
being used to ensure that it does not have excessive
capacitance
when
used
in
long
lengths.This
can
cause
a
temperature offset between what the controller
reads and
what the RTD actually measures. This again is
normally
not a problem since the controller compensates
for all
but the worst cases of this.
3. Unstable Temperature (Continued)
d) Check one by one if the all RTD leads are connected to
the
connector.
e) Lastly,it
is
possible
for
the
RTD
itself
to
fail
on
an
intermittent basis but this failure mode should be
considered unusual. This kind of failure is probably the
most difficult to find but fortunately it is also the least
likely as a failure mechanism.
9.3
Ground Fault
Ground fault warning /alarms can be caused by incorrect
installation as well as current leakage resulting from wet
system components
or
damaged
cables.
The CM2201/CM2202 Controller detects ground faults by
summing the
outgoing
and
return
trace
currents
through
an
internal current
transformer.Under
normal
operating
conditions
(no ground
fault
condition)
this
current
will
be
zero.
When
there is
a
flow
of
current
from
one
of
the
trace
supply
wires
to
ground, a
ground
fault
condition
occurs.
If a ground fault alarm is present on start-up of a new
installation it is likely due to a wiring error or damaged
cable. To verify this condition:
a) Check that the heating circuit neutrals return to
the
controller
and
are
not
connected
directly
to
the
distribution panel. This can be a common problem if the
installation is a retrofit situation.
b) On paralleled circuits, be certain that ALL neutrals
return. The late addition of a circuit may not be obvious
.
Note:
The controller monitors the integrity of the ground
fault(GF) detection. If afaultisdetected, thecontrollerwill
generate a GFI warning/alarm depend of the settings.
9.4
Common Warnings/Alarms - What to Look for
The CM-2201/CM-2202 has
a
wide
range
of
warning
and
alarming features that may be selectively enabled or
disabled
to
allow
the
monitoring
and
indication
of
trouble
conditions. Described below are the different warming and
alarm conditions available on the CM-2201/CM-2202, their
meanings, and possible causes. The warning settings must
be below alarm settings. If an alarm will be activated the
two SSR low power will be activated.
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