Dvp-120B - Macurco DVP-120B User Instructions

Typical coverage for CO, CO
gases (see the User Instructions for each sensor type for location and coverage details). Extra sensors may be needed near areas
where people work, such as toll booths. Macurco provides only the control panels and sensors. Fans, relays, and other devices are
provided by the contractor. See the appropriate building code for the size of fans and air changes per unit of time.
3.4.2

DVP-120B

A Modbus over Serial Line Cable should be shielded for best performance. The shield should be connected on each detector at SHD
terminal and connected to a ground terminal or chassis only at one end of the bus. An RS485-MODBUS must use a balanced pair (for
A-B) and a third wire (for the Common). For RS485-MODBUS, Wire Gauge must be chosen sufficiently wide to permit the maximum
length (1000 m or 3281ft). AWG 24 is always sufficient for the MODBUS Data. Category 5 cables may operate for RS485-MODBUS, to
a maximum length of 600 m 1968.5 ft. For the balanced pairs used in an RS485-system, wire with a characteristic impedance of higher
than 100 Ohms may be preferred, especially for 19200 and higher baud rates.
Note: It is recommended to always use twisted wires to reduce noise and allow for reliable data communication over greater distances.
Use at least 3-conductor wire with one twisted pair providing a pair for signal (A & B) and common (COM) connections.
For best performance use shielded 3-conductor wire with one twisted pair providing a pair for signal (A & B), common (COM) and shield
ground (SHD) connections.
3.4.2.1 Topology
An RS485-MODBUS configuration without repeater has one trunk cable, along which devices are connected, directly (daisy chaining) or
by short derivation cables. The trunk cable, also named "Bus", can be long. Its two ends must be connected on Line Terminations. (see
Line Termination - End of Line Resistor section). The use of repeaters between several RS485-MODBUS is also possible.
3.4.2.2 Length
The end to end length of the trunk cable must be limited. The maximum length depends on the baud rate, the cable (Gauge,
Capacitance or Characteristic Impedance), the number of loads on the daisy chain, and the network configuration (2-wire). For a
maximum 9600 Baud Rate and AWG26 (or wider) gauge, the maximum length is 1000m 3281ft. The derivations must be short, never
more than 20m 65.5ft. If a multi-port tap is used with n derivations, each one must respect a maximum length of 40m 131ft divided by n.
3.4.2.3 Grounding
The Common circuit (COM) must be connected directly to protective ground, preferably at one point only for the entire bus.
3.4.2.4 Power Wire
All field wiring is completed via modular connectors (provided). After wiring, simply plug the modular connectors into the matching
connectors on the MRS-485. The power connections to the remotely mounted detectors should be size AWG18 (minimum) for short runs.
Since Macurco detectors are rated for operation between 12 and 24 VDC or VAC, the voltage drop between the power supply and the
MRS-485 should not be an issue if the recommended power wire gauge guidelines below are followed. The terminals will accept wire
and NO sensors is 5,000 sq. ft. (464.5 sq. m), 900 sq. ft. (83.6 sq. m) for combustibles and other toxic
2 2
Figure 3-6 MRS-485 wiring
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