2-7
Installation
Thermocouple or
Millivolt Inputs In the case of thermocouples, make connections between the sensor and the
transmitter with thermocouple wire. For process mounting applications, connect
the thermocouple directly to the transmitter. For installations where the
transmitter is mounted remotely from the sensor, use appropriate thermocouple
extension wire. As with all low-level signal wiring, shielding is recommended for
long runs. Make input connections for the Model 444MV Millivolt Transmitter
using copper wires. The correct connections for thermocouple and millivolt
inputs are shown in Figures 2-6f and g.
Grounding The transmitter will operate with the current signal loop either floating or
grounded. However, many types of readout devices are affect ed by the extra
noise in floating systems. If operation appears noisy or erratic, grounding the
current signal loop at a single point may solve the problem. The negative
terminal of the power supply is the best place to ground the loo p. Alternately,
either side of the readout device could be grounded. Do not ground the current
signal loop at more than one point.
Thermocouple and millivolt transmitters are isolated, so the input circuit also
may be grounded at any single point (when a grounded thermocouple is used,
this point is the grounded junction), and the signal loop may be grounded at any
point.
The 444RL transmitter is not isolated, so there can be no grounds in the RTD
circuit. Since RTDs must be well-insulated from ground in order to give correct
temperature readings, this is not normally an installation limitation. The
positive side of the power supply should not be grounded for use with RTD input
transmitters. The 444RI9 should be used with grounded RTDs.
If using shielded wire, connect the shield of the sensor-to-transmitter cable to
the shield of the transmitters-to-receiver cable. Ground the shielding only a t the
signal loop ground.
Multi-ChannelInstallations
Figure 2-8 illustrates how several transmitters can be connected to a single
master power supply. In this instance, the system can be grounded only at the
negative power supply terminal. Since several channels are dependent on one
supply, an uninterruptible power supply or backup battery should be considered
if loss of all channels would pose operational problems. The diodes shown in
Figure 2-8 prevent unwanted charging or discharging of the battery.
FIGURE 2-8. Multi-Channel
Installation.
Transmitter
No. 1
Transmitter
No. 2
ToAdditional
Transmitters
Readout or
ControllerNo. 1
Readout or
ControllerNo. 2
Backup
Battery
dc
Power
Supply
+
+
–
–
444-0202A