© 2021 VPInstruments | MAN-VP-VP38-EN | Revision: 2100 | Date: 25-01-2021
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9
Electrical connections
NEVER USE AC POWER. THIS WILL VOID WARRANTY AND BRING PERMANENT
DAMAGE TO THE ELECTRONICS. THE INSTRUMENT MIGHT BE DAMAGED
BEYOND REPAIR.
CONNECT THE M8 CONNECTOR BEFORE POWERING UP THE INSTRUMENTS.
The VPFlowScope In-line 3/8" flow meter is equipped with a M8 5-pin connector which contains the
power input, an analogue output and a Modbus interface.
Pin
Signal
Wire color
1
+14 .. 24 VDC
Brown
2
0 Volt
White
3
4..20 mA signal, active
Blue
4
RS485 B
Black
5
RS485 A
Grey
* Wire colors apply to VPInstruments cables
M8 5-pin female connector
Cabling
Shielded twisted pair cabling must be used for proper communication and measurement. Connect
shield to safety ground on one point. The thickness of the wires depends on the cable length. For
cabling below 300 meter | 1000 ft, use 20 awg. For longer runs use 18 awg or better.
Power supply
The input voltage is 14 .. 24 VDC. Make sure that the power supply is at least 14 VDC at the
connector. Voltage drops will occur in long cables resulting in insufficient power. The display will
notify you when there is insufficient power.
9.1
4 .. 20 mA
An advantage of a current loop is that the accuracy of the signal is not affected by voltage drop over
the line. Even if there is significant electrical resistance in the line, the current loop transmitter will
maintain the proper current, up to its maximum voltage capability. The live-zero represented by 4 mA
allows the receiving instrument to detect some failures of the loop. An analogue current loop can be
converted to a voltage input with an external third party precision resistor.
The transmitter output is an active, non- isolated linearized current loop. This means that the + wire
is shared between power supply and the analogue output. A current will draw back from the
instrument to the power supply.
Cabling
3 wires are required to create a current loop. It is advised to use a shielded cable to prevent electrical
noise to affect the signal.
Ohm's law can be used to calculate the maximum distance. There are 2 parameters that needs to be
taken into account.
1. The voltage available is equal to the input voltage
2. The resistance depends on cable quality and length
