Wiring For Modbus - Quest Controls TELSEC MP2x User Manual

3.3.4 Contact Closures
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The TELSEC MP2x supports dry contact closures or wet contacts up to 65 VDC. A wet contact is an input
where there is an external voltage present. A dry contact has no voltage present and the MP2x provides
the sensing voltage. The detection points for determining ON/OFF status are greater than 2.8 VDC and
less than 0.8 VDC. There is no transition when the voltage is between these two values. Both wet and
dry input types are connected between the input terminal and a common terminal. For Wet inputs the
voltage must be between 0VDC and up to +65VDC. Negative voltages are not supported.

3.4 Wiring for Modbus

The MP2x has a serial port labeled COM 1 which is used to connect this device to a Modbus primary
polling device. The MP2x will listen for request and respond with the data being requested.
1. Connect no more than 32 Modbus devices per Modbus serial port
2. The maximum overall Modbus cable network length is 3,000 feet.
3. For normal applications, use Belden Cable #8102 or equivalent. This cable has two twisted pairs
and a separate foil shield. For applications requiring a more mechanically robust cable, use
Belden Cable #9842. This cable has two twisted pairs, a separate shield and a separate braided
shield.
4. Use one of the twisted pairs for the D0 (-) and D1 (+) connections and use the second twisted
pair for the C/Common connections. The cable shields must never be used for the C/Common
connections.
5. All the D0 (-) pins from every Modbus device on the network must be connected together. The
same is true with the D1 (+) pins, and the C/Common pins.
6. Connect the Modbus devices together in a daisy-chain configuration only. In this configuration,
the cable from the first Modbus device connector goes directly to the connector of the second
Modbus device, then from that connector directly to the connector of the third Modbus devices,
and so on. No star, ring or tree cabling network configurations, or additional cable stubs are
allowed.
7. Connect all the cable shields together so that they form one continuous connection from one
end of the Modbus cable network to the other. If a braided shield is also included in the cable,
then connect all of them together as well. If there is a mix of braided and non-braided shields in
the cabling network, then connect the braided shields together and then to the foil shields of
the nearest non-braided cable. At no time are any shields to be left floating.
Rev 2.1 10/21/21
Monitor Switch
Figure 5 - Wiring Contact Closures
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TELSEC MP2X User Guide