TROUBLESHOOTING
INCORRECT TEMPERATURE READINGS
Most incorrect temperature readings are due to errors involving the RTD’s and their connections to the
CT124. The following list contains suggestions to ensure the CT124 is reading the temperature correctly.
1.
Make sure that the proper RTD element is attached. For example, a CT124PD requires a PD-type
RTD for accurate measurement. Refer to the model number decoding information on page 23 for
RTD type compatibility.
2.
Use 3-lead RTD’s. Refer to the installation instructions concerning the connection of 2- and 3-
lead RTD’s.
3.
Check for proper 3-lead compensation; the resistance of the leads going to the RTD must be well
matched. For example, a difference of 1 ohm can mean more than 2.5°C (4.6°F) error for a
platinum RTD, or more than 26°C (47°F) error for a copper RTD. A good way to do this is to
measure the resistance between each leadwire while shorting the wires together at or near the
RTD. All 3 readings should match each other.
4.
Recalibration may be necessary (see page 20).
TEMPERATURE INSTABILITY
The CT124 display should show a stable reading and occasionally flip ±1 count under stable input
conditions. If your display changes by more than one digit, excessive electrical noise is being introduced
to the CT124, and fouling the measurements. There are a number of actions that may improve noise
immunity. A few things to try are:
1.
Use twisted and/or shielded leads for the RTD’s. If shielded wire is used, make sure the shield
is insulated from ground along its full length and makes only one connection at the CT124’s
terminal block.
2.
Make sure the RTD wires are routed away from noisy sources.
Refer to the RTD wiring
instructions on page 7.
3.
Look for other equipment operating off the same branch circuit that may emit electrical noise.
Nearby motors, contactors, or computer equipment may emit electrical noise through the power
line that overpowers the noise filtering circuits inside the CT124. Look for an alternative branch
circuit for the CT124 or place a line filter between the power source and the CT124.
4.
Disconnect the earth ground at the power terminals on the rear connector board of the CT124.
Because the CT124 case is made of a plastic, this ground is not required for safety reasons.
Removing it may eliminate some capacitively coupled noise.
NO DISPLAY
1.
Make sure that the internal power supply switch is set for the appropriate voltage. See Figure 3.
2.
Read the safety precautions on page 2 and check internal and external fuses or breakers (see page
5). Replace blown fuses with identical ones.
If the previous suggestions did not reveal the source of the problem, please contact MINCO for help.
Information about our return/loaner/exchange program is on page 21.
Minco Products, Inc.
CT124 Instruction Manual
19
Summary of Contents for CT124
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