© 2021 VPInstruments | MAN-VP-VP38-EN | Revision: 2100 | Date: 25-01-2021
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Example:
Input voltage
24 V
Required maximum current
20 mA
24 V / 0.02 A = 1200 Ohm
1200 Ohm is the maximum load that can be applied with a 24 V input level.
Above example does not include the current consumption of the flow meter itself. When power to the
flow meter is applied using a long cable, include a current consumption of 500mA to the formula.
Electrical scheme
The current meter is placed in between the current output and the power supply ground. You can
also use a digital multimeter to test the current output.
9.2
RS485
Installing a RS485 network require specific knowledge. Not following the specifications
strictly might result in in-correct communications and equipment damage. Please leave
installation up to professional contractors. Make sure that they read this chapter
carefully and follow up all RS485 guidelines.
RS485 is a differential balanced line over twisted pair. It can span relatively large distances up to
1200 meter | 4000 feet. The wires should be connected as a point-to-point configuration, or also
called daisy chain. Do not install as star or ring network! The trunk line goes from the master to all
devices making a drop down to each device. The cable length from the trunk line to the Modbus
device needs to be as small as possible. Junction boxes are used to make the T junction.
