© 2020 Van Putten Instruments BV | MAN-VP-V-UK | Revision: 2000 | Date: 29-7-2020
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last Modbus Junction box in the daisy chain.
Biasing
When there is no data activity on an RS485 network, the communications lines are "floating" and,
thus susceptible to external noise or interference. Receivers on a RS485 network have built in
hysteresis (200mV differential required to insure known state). To insure that a receiver stays in an
inactive state, when no data signal is present, bias resistors are required. Bias resistors are a pull-up
resistor on Modbus B and a pull-down resistor on the Modbus A line. The value of the bias resistor
depends on the number of devices and the supply voltage. The table below shows which resistor
values can be used for different voltage in a chain with 1 to 8 VPFlowScope probes.
Supply voltage
Bias pull up
Bias pull down
12 V
5 KΩ
1 KΩ
24 V
10 KΩ
1 KΩ
5.3
Analog input connection
Analog sensors can be connected to the analog I/O converter. We have chosen for 4..20 mA as
default interface. If needed, you can change the I/O converter to 0..10 Volt.
I/O converter description
This converter contains 8 inputs. Internally, you can find dip switches which affect the analog input
configuration. It can be set to 4..20 mA (default) or 0...10 Volt.
Connecting an analog sensor
The analog input converter measures the current in the loop. This means that it needs to be in
between the loop. The 24V terminal inside the VPVision-M can be used to supply power to the
sensors.
Powered loop
Active output
VPLog-I
Pressure sensors
VPFlowScope analog output
Dew point sensors
5.4
VPN connection
For safe remote access to the VPVision-M without interfering with the client's network, a VPN router
is mandatory. Nowadays, most industrial sites provide a VPN for their employees. The only thing
they need to configure is the remote access to the IP address of the VPVision-M. This VPN
connection enables us to provide remote support. The VPVision does not send out or retrieve any
