Instruction manual

ControlWave GFC IS Communication Interface Manual (CI-CW-GFC-ISTRAN)
Issued Nov-09 System Wiring 3-1
Chapter 3 – System Wiring
This chapter includes details on grounding and wiring for the IStran.
3.1 Introduction to System Wiring
The IStran connects a radio, modem, or other communications device to
a ControlWave GFC-IS Flow Computer/Corrector. An IStran can also
provide an intrinsically safe interface between an external power supply
and RS-232 signals associated with a radio, modem or ControlWave
RTU (in a non-hazardous area) and a ControlWave GFC-IS in a Class I,
Division 1 area.
3.2 Grounding
The IStran provides up to 500V of isolation between the hazardous and
non-hazardous interfaces. When using the ground isolation capability of
the IStran, devices on either side require separate power sources, and
each source must power the corresponding IStran interface. Refer to the
field wiring diagrams in Section 3.4 for systems with independent power
sources.
When isolation is not required, a single power source supplies both
IStran interfaces and, optionally, both connected devices. To power both
IStran interfaces using a single power source, connect the power source
between NPIN and NGND. Use connector HJ2 (see Figure 1-4) as a
jumper position to wire HPOUT to HPIN and HGND to CGND. Note
that CGND and NGND are internally connected, and that CGND is
connected to the IStran case. Refer to the field wiring diagrams in
Section 3.4 for systems with a single power source.
When a ground connection already exists between the power source and
the ControlWave or communications device, do not wire the ground
terminal on the IStran communications connector (NJ1 or HJ1). The
ground reference established on the IStran power connector (NJ2 or
HJ2) serves as both power supply return and signal ground reference.
Wiring the communications connector ground terminal may introduce a
ground loop and degrade the performance of the IStran under these
circumstances. The wiring diagrams in Section 3.4 illustrate the
recommended practices.
For intrinsic safety applications, you must use redundant earth grounds.
Both grounds must measure less than one ohm to earth. The NGND
terminal provides one ground, and the case provides the other. If the
mounting panel does not provide a suitable ground path, connect a
12AWG or larger ground conductor to one of the IStran mounting
screws.