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Power Supply and Output Wiring continued
4.4.1
Milliamp output
The 4–20 mA output is an active output that can represent the mass or volume flow rate. At the
factory, the output is configured to represent the range of flow rates that are measured in the
application. The milliamp output is active, does not require external power, and has the following
features:
•
Can supply any loop-powered process indicator.
•
Isolated to ±500 VDC from all other outputs and earth ground.
•
Requires loop resistance of 250 to 600 ohms to produce digital signals for communication via
HART protocol.
•
For milliamp output, the negative terminal can be grounded or left floating. If the output
communicates via HART protocol, the negative terminal should be grounded for optimal
performance.
Milliamp output performance is described below and illustrated in Figure 4-3.
In compliance with the NAMUR NE43 standard:
•
To represent process data, the milliamp output will produce a live signal in the range of
3.8–20.5 mA.
•
The milliamp output will never produce a signal in the range of 2.0–3.8 mA, or in the range of
20.5–22 mA.
•
To indicate a fault, the milliamp output will produce a signal of 2 or 22 mA. The fault output
level is determined by the fault-output jumper setting — downscale or upscale — as described
in Section 2.3.2.
Figure 4-3
Milliamp output performance
2
3.8
22
Milliamp output range has changed.
Milliamp outputs will not output live signals between
2.0 and 3.8 mA, or between 20.5 and 22 mA.
Systems that rely on milliamp output signals in the ranges
listed above might not perform as expected. For IFT9701
transmitters shipped after October 1999, outputs will
saturate at 3.8 and 20.5 mA, unlike previous versions of
IFT9701 transmitters.
Reconfigure systems as necessary.
Downscale
fault indication level
Operating range (live signal)
CAUTION
fault indication level
Output in mA
Upscale
20.5
Model IFT9701 Transmitter Instruction Manual
22
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