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DI-900 Modbus Distributed Data AcquisitionFrequency/Pulse Counter Modules
Periodic or Pulse Waveform Input
Limit Alarms or Discrete Outputs

  • Standard Modbus RTU protocol with high-speed RS-485 communication (up to 115K bps)
  • Separate microcontrollers on each channel for pulse counting and period measurement
  • Solid-state relay outputs enable local limit alarms or host-controlled on/off switching
  • Bipolar and unipolar input signal support
  • Programmable pulse counter functions
  • Input filtering functions include hysteresis, averaging, debounce, relay time delay, and alarm deadband controls
  • 4-way isolation (input, output, power, network)
  • Watchdog timers provide a failsafe output
  • Self-diagnostics monitor microcontroller activity to detect operational failures (lock-up) and execute a reset to restore communication.

Data Sheet


Product Highlights

This signal conditioner is a two-channel analog input module with discrete outputs and Modbus communication. It conditions periodic or pulse waveform inputs and provides solid-state relays for limit alarms or ON/OFF control.

Versatile inputs accommodate many applications using TTL, magnetic pickups, proximity sensors, or a variety of switches (high/low-side transistor, dry contact, open drain, open collector). Bipolar and unipolar waveforms are supported with a selectable input bias that accepts both zero and non-zero crossing signals. Voltage threshold and relative hysteresis are also user selectable.

Inputs may also function as event counters with separate microcontrollers for each channel. The module counts pulses on the positive or negative edge. It can wrap around to zero for continuous counting, latch at a programmed count value (setpoint), or automatically reset itself to zero after reaching a setpoint value. Software controls enable remote resets. A variety of filters help remove noise, jitter, and other mechanical effects to prevent false counts.

The discrete outputs can operate as independent alarms or provide on/off control regulated by the host system. As limit alarms, each output can be set for high and/or low setpoints exclusively tied to an analog input. These low cost modules are ideal for standalone alarms as well as for local backup of the primary control system. See the Circuit Connection Diagrams.

Everything you need to complete your network is available from DATAQ Instruments, Inc. - isolators, signal converters, signal boosters, power sources, and mounting hardware. Check out the Accessories.