However, in some instances, the user may wish to interface to 4-20mA analog signals that are proportional to flow. Replacement of Sensus ACK-PAK instrumentation is just one possible use. However, in this case, the EtherMeter is capable of deriving the 4-20mA signal from either an encoder-type or a pulse-output-type flow meter. Within the Setup Menu, the EtherMeter also permits the user to specify the 4-20mA span (the flow-rate that corresponds to 20mA).
When used with an encoder-type flow meter, it is important to recognize the limitations of this type of 4-20mA signal. Because it is not based upon a hard real-time flow-rate signal, the user should therefore exercise caution when using the 4-20mA signal to drive a PID control loop.
This document describes the wiring procedures and EtherMeter settings that are required for 4-20mA output signaling. Note that the EtherMeter requires Special Firmware plus an ADAM-4024 module (by Advantech) for this option, and so the purchaser must ensure that the Analog-Output Firmware+Module option is selected when buying at the eStore. Also, it is important to note that when using this option, the ADAM-4024 module consumes the serial port; and therefore any digital communications to the EtherMeter must occur via the Ethernet port.
Detailed procedures are available in a new Application Note posted in the SCADAmetrics Documentation Center: