Rules For Proper Installation; Wiring And Power Supply; Maximum Loop Load In Relation To The Power Supply Voltage - CEMB TR-NC/8 Manual Del Usuario

4.

Rules for proper installation

Measurements made using no-contact sensors that exploit the eddy current principle may be compromised or
falsified by a series of phenomena or parameters which should be taken into consideration when designing the
monitoring system.
4.1

Wiring and power supply

The monitoring instruments require an external power supply which should as directly as possible branch off from a
reliably efficient source also in cases of emergency of the main electric systems.
Power supply from a low-voltage network used for other instruments should be avoided, as their failure might place
the auxiliary supply network out of service and hence also the monitoring instruments.
If the power supply is necessarily centralized for various instruments, suitable devices should be installed so that
failure of a single instrument or amplifier or transmitter cannot affect the power supply to the other instruments.
Use a bipolar shielded cable; the cross-section of the conductors is related to the distance between the transmitter
and the acquisition system. If the distances are considerable, take into account the sum of the voltage drops on the
load and on the cable, which must ensure proper power supply to the transmitter. The nominal supply voltage is 24
VDC. The transmitter can also measure correctly with a voltage between 24 and 35 VDC, guaranteeing a maximum
loop load value (sum of the measurement resistance plus the cable resistance) as shown in the graph below.
4.2

Maximum loop load in relation to the power supply voltage

700
600
500
400
300
200
100
0
16 18 20 22 24
Power supply [V]
26 28 30 32 34
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