Optional 4-20 Ma Current Output - Teledyne HFM-301 Instruction Manual

301/303/305/306/307 Flowmeters and Controllers Instruction Manual

Optional 4-20 mA Current Output

An option to the standard 0-5 VDC output is the 4-20 mA current output that is proportional to flow. The 4-20
mA signal is produced from the 0-5 VDC output of the flow meter. The current loop output is useful for remote
applications where pickup noise could substantially affect the stability of the voltage output or long cable runs
where cable resistance would cause a voltage signal to decay.
The current loop signal replaces the voltage output on pin 6 of the DA-15 connector. The current loop is
sourced internally from the +15 VDC supply and must be returned to either the signal common (pin 5) or the
supply common (pin 9) after passing through the monitoring circuitry to complete the loop. If returning the
current to pin 5 (signal common), the load must be between 0 and 600 ohms. If returning current to pin 9
(supply common), the load must be between 600 and 1200 ohms. Failure to meet these conditions will cause
the current transmitter to fail.
The 4-20 mA I/O option can accept a current input for flow controllers. The 0-5 VDC command signal on pin 14
can be replaced by a 4 - 20mA command signal. The loop presets an impedance of 75 Ohms and is returned to
the power supply through the valve common.
EAR99 Technology Subject to Restrictions Contained on the Cover Page
Current Return Pin Load Resistance R Ω
5 (Signal Common)
9 (Negative Rail)
0<R<600
600<R<1200
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