16
54-610 Thermatel
®
Model TD1/TD2 Flow Level Switch
Each element of the sensor is a miniature RTD (Resistance
Temperature Detector). One element measures the tem-
perature of the process, providing a reference temperature.
The second RTD is self-heated to establish a temperature
differential above the reference temperature. The cooling
effect on the heated RTD, caused by the presence of flow
or level, decreases the differential temperature between the
two RTDs. When the temperature difference reaches the
set point, the relay will change state. Sensor designs are
suitable for operation in temperatures of -100 to +850 °F
(-73 to +454 °C).
3.3
Fault Detection
The TD1 and TD2 have continuous self diagnostics to
ensure the signal from the sensor is within a select range. If
the electronics detect an out of range signal, the switch
will go into fault mode.
In the event of a fault, the red LED will blink and the
relay will de-energize. In the TD2, the mA output will go
to less than 3.6 mA if low level fail-safe is selected or
greater than 22 mA if high level fail-safe is detected.
If a fault is detected, refer to
3.5 Troubleshooting
.
3.4
Resistance Values
The following tables provide the expected resistance values
for the sensor. Refer to the indicated figures for pin locations.
Refer to
3.6.2 Probe Replacement
for removing bezel and
circuit boards.
Pin
Expected Resistance
1 to 3
90 to 180 ohms
(275 ohms with high temperature probe)
2 to 4
90 to 180 ohms
(275 ohms with high temperature probe)
TD1 (see Figure 12)
Pin
Expected Resistance
1 to 3 or 4
90 to 180 ohms
(90 to 275 ohms with high temperature probe)
2 to 5 or 6
90 to 180 ohms
(90 to 275 ohms with high temperature probe)
1 to 2, 3 to 4,
5 to 6
0 to 12 ohms
TD2 – Integral Electronics (see Figure 13)
TD2 – Remote Electronic Enclosure (see Figure 14)
1 2 3 4 5 6
Shield
Figure 14
TD2 Remote Probe Connections
1
4
1
4
Unmarked Wires
Marked Wires
Figure 12
TD1 Probe Connections
1
6
1
6
Unmarked Wires
Marked Wires
Figure 13
TD2 Probe Connections
