header valves
Valves & Actuation


The ModBus option module has been specifically designed for use with the DHC-100 Positioner via plug and socket installation. This module provides an isolated RS-485 bus connection using the ModBus protocol. The on-board screw terminal strip provides easy connection to the bus (Terminals A, B, & Common). With an input impedance of 96K ohms, up to 256 units can be connected on the bus. On-board dip switches alow configuring the module for various bus settings: mode, baud rate, parity, node address, and line terminating resistor.

Ideal Applications Include:


Bus Connection:

Type: ANSI TIA/EIA RS-485 (electrically isolated up to 1500 Vrms)
Protocol: ModBus (selectable RTU or ASCII mode)
Logic “1”: +VBA
Logic “0”: -VBA
Selectable Address: 0-255 (1 to 247 usable)
Selectable line terminating resistor (RBA): 150 ohm
Line Polarization: Not required


Operating Temperature Range: 0C to 60C
Storage Temperature Range: -40C to 85C
Relative Humidity Range: 0 to 90% (noncondensing)

Transmitter Output:

Differential Output Voltage (VBA):
5V Max @ No load
1.5V min @ 54 ohm load
Output short circuit current:
A to B: 95mA typical
A or B to COM: 113mA typical

Transmitter Input:

Input Impedance (RBA): 96K ohms min (1/8 node)
Input Logic Threshold Voltage (VBA): 30mV min, 200 mV max
Input Hysteresis: 20mV Typical

Cable Characteristic Impedance:

A value of 100 ohms or greater may be preferred, especially for 19.2K and higher baud rates


  • ModBus option module plugs directly into DHC-100 positioner card
  • Selectable RTU or ASCII mode
  • Selectable Even parity or no parity
  • Selectable baud rate: 9600,19.2K, 57.6K, 115.2K
  • Node Address Setting: 0-255
  • Selectable line terminating resistor