©201
7
Nelson Heat Tracing Systems
www.nelsonheaters.com
GA2497 Rev.
5
CM-2201/CM-2202
Troubleshooting
9.1
Troubleshooting
9.2
Operator Checks
Upon
receipt
of
the
controller,
or to check the controller
for
an indication of normal operation, follow the
operational procedures shown below.
T
hese
procedures
are
designed
to
f
amiliarize
the
operator
with
the
controller
and
to
provide
an
understanding of its operation.
In
order
to determine if a fault is associated with the heat
tracing, wiring
or the
controller,
it
will
be
necessary to
troubleshoot
the
wiring
and
tracer
circuit.
If
the fault
remains,
remove
power
from
the
controller
and
exchange
it
with
another
controller. This
may
require
some
reprogramming
of the new CM2201/CM-2202.
Refer
to
the following sections
for
the
appropriate
topic.
9.2.1
RTDs
RTD
failures
after
installation
can
generally
be
attributed
to incorrect wiring or improper installation of the sensor.
Troubleshooting of these failures is a very simple
procedure if the proper steps are undertaken in the
correct order.
Some specific
RTD
problems
and
the
correct
methods for troubleshooting are outlined as follows.
1. RTD Failure Alarm(s)
If the CM2201/CM-2202 controller indicates a failure of an
RTD:
a) Ensure that the RTD is a 3-wire 100 (Platinum
Type).
TURN THE POWER TO THE CONTROLLER
OFF
BEFORE
PROCEEDING!
b) Disconnect the RTD wiring from the input terminals.
c) Measure the RTD’s resistance between the source
(RED)
and sense (RED) leads at the controller (it should
not
exceed 40 Ω). Excessive lead resistance will cause
a RTD
FAILURE ALARM and must be corrected. Look for
loose
terminals,
excessive
lead
length,
or insufficient wire
gauge and correct as necessary.
d) Measures the RTD’s resistance between the source
(RED)
or sense (RED) lead and the common (WHT) lead
of the
RTD at the controller (should be between 60
and 330 Ω
depending
on
the temperature and the lead
resistance.
Verify that the
RTD is wired correctly
—the
heat tracing
conrtrollers will always be terminated in
the
order: source
(RED), common(WHT), sense
(RED).
When wiring to the
CM2201/CM2202, the terminals are marked
as follows:
Terminal No.
Description
GND Bus
Shield
RA
RTD A Source (RED)
WA
RTDA Common (WHT)
RA
RTDASense(RED)
GND Bus
Shield
RB
RTD B Source (RED)
WB
RTDBCommon(WHT)
RB
RTDB Sense (RED)
The
RTD
manufacturer
will
typically
color
code
the
leads with
the source and sense being the same color, and the
common
a
different
color. Ensure
that
the RTD
extension
wire
shield is terminated at one end only, normally using the
terminal block provided at the terminal board.
Note:
Some
manufacturers
use
the
common
Black-White-Red
triad
color
code
f
or
the RTD
connections. Usually, the RED
lead is the common connection (same as the White-White-
Red color scheme) and the White and Black connections may
be used interchangeably.
2. Temperature Verification
If you consider that the indicated or displayed temperature
is not correct, thecontrollerandthe RTDcanbequickly
checked for correct operation. To
verify
the
RTD:
TURN THE POWER TO THE CONTROLLER OFF BEFORE
PROCEEDING!
a) Disconnect the RTD wiring from the input terminals.
b) To
calculate
the
temperature
indicated
by
the RTD,
measure
the
resistance
from
source
(red
wire)
or sense
(redwire) to
common (white wire) and subtract
the
resistance
measured
between
source
and
sense. This
will
give a compensated resistance value that can be
cross- referenced
to
one
of
the
RTD
tables
found
in
A
ppendix
E or Appendix F.
Compare
the
measured
resistance and
cross-referenced temperature value
obtained from the
RTD
table
to
the
indicated
or
displayed
value.
These should
agree
to
within
the
accuracy
standards
of
the
CM2201/CM2202 and the RTD.
20
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