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141-072011 - 201/203 Series Page 6 of 23
1.4. 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 (pin 2 of DE-9
24 Volt). The current loop is sourced internally from the +15 VDC supply and must be returned to
the signal supply common after (pin 5 [±15VDC] or pin 8 [24 VDC]) passing through the
monitoring circuitry to complete the loop. The load must be between 0 and 600 Ohm.
The 4 - 20 mA I/O option can accept a current input for flow controllers. The 0 - 5 VDC command
signal on pin 14 (pin 3 for 24 Volts) can be replaced by a 4 - 20mA command signal. The loop
presents an impedance of 50 Ohms and is returned to the signal common. On the 24 Volt units, the
signal common will need to be tied to the power supply common external to the flow controller to
complete the loop since the signal common is galvanically isolated internally from the supply
common. This line must be current limited (<50 mA) to prevent short circuit currents from
damaging the receiving circuit in the flow controller.
1.5. Other Accessories
1.5.1. Hastings Power Supplies
Hastings power supply/display units are available in one and four channel versions. They convert
100, 115 or 230VAC to the ±15 VDC required to operate the flow meter and provide a digital
indication of the flow rate. Interface terminals for the retransmission of the flow meter analog output
signal are located on the rear of the panel.
The THCD-100 and the THPS-100/400 models are built with controllers in mind but will work
with meters as well. The Model 40 is for flow meters only. Throughout this manual, when
reference is made to a power supply, it is assumed the customer is using a Hastings power supply.
Hastings THCD and THPS power supplies are CE marked, but the Model 40 does not meet CE
standards at this time. The Model 40, The THCD and THPS-100 are not compatible with 4 – 20
mA analog signals. With the THPS-400, individual channels’ input signals, as well as their
commands, become 4 – 20 mA compatible when selected. The THPS-400 also sports a Totalizer
±15 Volt Supply
24 Volt Supply