4A/4AO MODULE (4-20mA OPTION)
Available only on the digital models 758II, 759II, 753II and 754II, or all analog and digital OEM Monitor/controllers.
-4A 4-20mA Self/Remote-powered Isolated output module ordered with Monitor/controller.
-4AO 4-20mA Self/Remote-powered Isolated output module ordered separately (includes harness).
1. DESCRIPTION
The 4-20mA option gives the Series II Monitor/controller the ability to send a signal very long distances with minimal interferences and signal degradation. The output is an Isolated 4-20mA signal that corresponds to the full scale range of the Monitor/controller into which it is installed. This output is easily confi gured to be either self-powered or remote-powered as required for your particular application.
NOTE: The maximum impedance of the user’s current input instrument should not exceed 600 ohms.
Since the output is an isolated current loop, it is the ideal choice for applications requiring; a control signal to be run very long distances, systems requiring a 4-20mA input or in instances where isolation is necessary. As the output is isolated, and a current, it is useful for long distance interface, especially where wiring resistances may be high, and/or the ground potentials may differ between the sensor input ground and the current receiving instruments ground.
The 4-20mA output will not be degraded in accuracy even when the ground differences are as much as 120VAC @ 60Hz. Interface wire resistance of 350Ω will not degrade the accuracy of the output when interfaced to a typical 250Ω input impedance of a transmitter current input device.
The output is capable of driving a minimum of 600Ω worse case, therefore, will satisfy virtually all modern interface requirements. Current input devices usually have an input impedance of 250Ω, however, some older designs can have as high as 500Ω or as low as 10Ω. This “-4A” option will drive any impedance from 0 to 600Ω without any degradation of performance.
There are two modes in which current loop transmitters operate; Self-Powered and Remote-Powered. Self-Powered — the transmitter provides the power to drive the 4 to 20 mA current. See fi gure III.B.1. Remote-powered — the receiving instrument provides the power to drive the 4 to 20 mA current. See fi gure III.B.2.
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