Chapter 2.
36
Model CTF878 Startup Guide
2.1.14 Option Card Wiring
2.1.14.1
Wiring an Alarms Option Card
The CTF878 flowmeter can accommodate up to 4 alarm option cards. Each alarms option card includes three
Form
C relays (designated as A, B and C).
The alarm relays on the option card are available in two types:
•
general purpose
•
hermetically sealed for Class I, Division 2 hazardous areas.
The maximum electrical ratings for the relays are listed in Chapter 4,
Specifications. Each of the three alarm relays
can be wired either as
Normally Open (NO) or Normally Closed (NC).
In setting up an alarm relay, it may be wired for either
conventional or fail-safe operation. In fail-safe mode, the
alarm relay is constantly energized, except when it is triggered by a power failure or other interruption. See Figure 21
below for the operation of a NO alarm relay in both conventional and fail-safe mode.
Connect the two wires required for each alarm relay in accordance with the pin number assignments shown in
Figure 21: Conventional and Fail-Safe Operation
2.1.14.2
Wiring a 0/4-20 mA Analog Inputs Option Card
To calculate the standard volumetric flow rate of natural gas, the CTF878 requires accurate
temperature and
pressure data from the measurement site. Transmitters installed on the pipe can provide this information via an
optional 0/4-20 mA analog inputs card. This option card includes two isolated 0/4-20 mA analog inputs (designated
as A and B), each of which includes a 24 VDC power supply for loop-powered transmitters. Either input may be used
to process the temperature signal, while the other input is used to process the pressure signal.
Conventional
not triggered
NO
C
NC
not triggered
Fail-Safe
NO
C
NC
ALARM
MONITORING
DEVICE
DEVICE
MONITORING
ALARM
triggered
Conventional
NO
C
NC
NC
C
NO
ALARM
MONITORING
DEVICE
DEVICE
MONITORING
ALARM
or power failure
Fail-Safe triggered
Summary of Contents for CTF878
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