kajaaniMCA
i
– Installation, Operating & Service - 11.3 - W4610201 V2.5 EN
Table 11.1. Resistance values of the Pt-100 sensor.
Temperature measurement error
Process temperature measured by the sensor is below
0°C (32°F). Possible causes:
• Pt-100 sensor connector is disconnected from the
Field Connection Board,
• defective Pt-100 sensor cable,
• defective Pt-100 sensor,
• fault in Electronics Unit.
First make sure that the Pt-100 sensor connector is
securely connected to the Field Connection Board,
connector P4. If this connection is OK, connect a Pt-100
simulator to replace the Pt-100 temperature sensor. The
temperature measured by MCAi must be within ± 2°C
(± 3.6°F) of the reading marked on the simulator. If not,
the Electronics Unit is faulty. Replace the Electronics
Unit and perform a new start-up as instructed in section
6.A or in chapter 12. (HART communicator).
If the MCAi sensor measures the Pt-100 simulator
correctly, either the Pt-100 sensor, its cable or connec-
tor is defective. Replace the Pt-100 sensor (see section
11.C.5).
The Pt-100 sensor and wires can be checked with a
multimeter, as follows:
1. Switch power off from the MCAi, either by switch-
ing the supply power off or by disconnecting the
power ground connector from the Field Connection
Board.
2. Measure the resistance of the Pt-100 sensor from its
pins soldered to connector P4 (on Field Connection
Board).
Two red wires and two white wires are connected to
the connector. The wires must be connected alternately:
red – white – red – white. It does not matter which color
comes first.
The red wires are connected together at the Pt-100
sensor, and the resistance between them must be < 2
Ohm (wire resistance). If the resistance is infinite, the
wire is either broken or come loose from the connector.
If you cannot locate the break in the wire, contact the
supplier’s service.
Also the white wires are connected together, and the
resistance between them must be < 2 Ohm. If the
resistance is infinite, the wire is either broken or come
loose from the connector. If you cannot locate the break
in the wire, contact the supplier’s service.
The resistance between any wire and ground (sensor
body) must be > 1 MOhm. If there is a short circuit, the
wire insulation is faulty. If you cannot locate the faulty
point, contact the supplier’s service.
If all of the above tests show that the wires are OK,
the Pt-100 sensor is faulty. Contact the supplier’s
service.
Measurement Resistance
Between the 2 red wires
and between the < 2 Ω
2 white wires
Between GND and
any wire of Pt-100 >1 MΩ
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