G-Tek Corporation Private Limited
13
5.1.1.2
Sensor Wiring
To ensure maximum LmNet performance, proper wiring installation practices must be followed.
Failure to do so can result in a range of problems, from loss of configuration to component failure,
caused by transmitted or radiated electrical noise. Proper consideration must be given to local noise
sources and appropriate suppression steps taken to minimize any potential problems.
Among the most common sources of noise are: Relays, SCRs, valve solenoids, electric motors, power
line disturbance, wire-to-wire coupling, electrostatic discharge (ESD) and radio-frequency interference
(RFI).
1.
To achieve the best results, the following notes should be considered:
Low level signal wiring such as that associated with thermocouples, RTDs and current loops
should always be kept separate from power and control output wiring.
2.
Signal input wiring should be twisted pairs/triplets etc. and the conductors should be stranded
rather than solid in construction. All signal wiring should use ground-shielded wires or be routed
through grounded conduit. This minimizes the effects of RFI and ESD.
3.
Special care should be taken when wiring to relay or solenoid coils, as large transients are
produced when coils (or any other inductive devices) are switched. This problem can be
eliminated using suitable suppression devices across the coil. Coil transients can also be
transmitted through the air, so the recorder itself should be mounted as far as possible from
power control devices and/or wiring.
4.
When line power is poorly regulated and / or subject to voltage surges or transients,
consideration should be given to the use of a line conditioning/transient suppressing line power
regulator. Process control motors, valves, relays, and heaters should not be connected to the
same power lines that are used for instrumentation.
5.
The connection of the LmNet to a proper safety earth ground is essential. Such a connection not
only reduces the possibility of electric shock, but also provides the required return for the LmNet
line power filters.
6.
All local electrical codes of practice must be followed when installing any instrumentation. For
sensor wiring, all the sensor connectors are at the back side of the LmNet as shown in figure 9.
