RM-4DI2-4AI2 Usage Tips

This module is an ideal solution for small I/O locations with just a few inputs which may be a combination of discrete (switch closure) inputs, 4-20 mA process signals and pulse accumulator channels.

Slow / Fast Response – Discrete Inputs

Select fast response for minimal input filtering to respond to DC input changes in 5 mS. Slow response looks for stable inputs for approximately 25 mS to filter contact bounce (important when counting mechanical switch closures) in noisy environments.

Pulse Counters

Enable pulse counters to increment an analog input register (SIXNET address AX4-AX7 or Modbus address 30005 - 30008) each time an OFF to ON transition occurs on the corresponding discrete input (X0 - X3 or Modbus address 10001 - 10004). These counters report unsigned 16 bit values (0 - 65535) and are volatile (forget their counts if power is lost). These counters cannot be reset under software control. Typically, retention of the values and resetting the counts is accomplished in software at the host computer that polls these inputs.

High Speed Counter

The first channel (and only the first channel) may be configured as a high speed counter to record pulses as fast as 2 KHz. In this high speed mode, the input filtering is not active, and even short input spikes will most likely be counted.

Field Replaceable Current Shunt

Each 4-20 mA input channel has a 100 ohm precision shunt across its input to develop a 2 volt signal when a full scale 20 mA input is applied. This shunt is located in the module’s base, giving you the advantage of maintaining a continuous circuit even if the module is removed from the base. If excessive voltage is applied to an input, this shunt will blow like a fuse to protect the circuit. These shunts are installed in sockets to allow easy field replacement. A spare shunt is provided for your convenience. These shunts are precision devices that should only be replaced with authorized factory replacements.

Open Loop Detection

This module can detect and report an open instrumentation loop on its input. By allowing the module to report a negative value if the current falls below 4 mA, low limit logic in your DCS, PLC, RTU or computer can signal the loss of current. To enable this feature, select the "Go Negative Below 4 mA" setting for each individual channel.