What Is a High-Speed Counter and High-Speed I/O Module? Selection Criteria
A high-speed I/O module is a PLC module that counts encoder pulses normal inputs miss, or sends high-frequency pulses to stepper and servo drives.
A high-speed I/O module is a PLC module that counts high-frequency pulses which the PLC's normal digital inputs miss because of the scan time (high-speed counter, HSC), or sends high-frequency pulses to stepper and servo drives for positioning (pulse output). A high-speed counter counts the pulses from an encoder independently of the PLC program, so position, length and speed are measured without missing pulses. Cut-to-length control, conveyor tracking, filling and packaging machines are typical applications.
Modules in the catalog
| Model | Function | Channels | Information in the product data |
|---|---|---|---|
| Delta AX-502HC10-0A | High-speed input | 2 | 500 kHz, source type, NPN digital input |
| Delta AX-502PU01-0A | High-speed pulse output | 2 | 500 kHz, sink type, NPN digital output |
| Schneider Electric BMXEHC0200 | High-speed counter | 2 | 32-bit, 6 inputs and 2 outputs per channel, IP20 |
| Schneider Electric BMXEHC0800 | High-speed counter | 8 | 16-bit, 2 inputs per channel, 24 V DC |
The Schneider modules are for the Modicon M340 platform. Check in the datasheet which PLC family the Delta modules are used with.
Selection criteria
- PLC family: The module fits into the PLC's rack or expansion slot; only modules of the same family can be used.
- Frequency: The highest pulse frequency is the encoder's pulses per revolution times the speed. For example, a 1000-pulse/rev encoder at 3000 rpm produces 50 kHz; with quadrature (x4) counting the count rate the module handles rises. The module's limit must be above this value.
- Resolution and channels: For long runs and high pulse counts, a 32-bit counter (BMXEHC0200) counts longer without overflowing. For many simple counting points, the 8-channel BMXEHC0800 is suitable.
- Input and output type: An encoder or sensor with an NPN output connects to a source (current-supplying) input; one with a PNP output to a sink input. For pulse output, check whether the drive's pulse input is sink or source type.
- Counter functions: Functions such as direction detection (A/B phase), reset input and compare output determine the number of inputs and outputs per channel; the 6 inputs and 2 outputs per channel of the BMXEHC0200 serve these tasks.
Common mistakes
- Connecting fast pulses to a normal input: Pulses shorter than the scan time are missed and the count falls short.
- Not checking NPN/PNP matching: The input never detects or appears permanently active.
- Running the encoder cable unscreened in the same duct as power cables: Interference produces false pulses; use screened cable and earth the screen at one end.
High-speed I/O modules at Welibaba
The High-Speed I/O Modules category has 4 active products: the Delta AX-502HC10-0A and AX-502PU01-0A are listed with prices, and the Schneider Electric BMXEHC0200 and BMXEHC0800 are sold on quotation. The devices driven by pulse outputs are in the Stepper Drives and Servo Drives categories; other modules are explained in the PLC input and output modules guide.
Frequently asked questions
What does a high-speed counter module do?
It counts high-frequency pulses from an encoder or sensor independently of the PLC scan, measuring position, length and speed without missing pulses.
Is a normal PLC input not enough for an encoder?
It can be at low frequency. When the pulse duration approaches the PLC scan time, pulses are missed; then a high-speed counter is needed.
What is the difference between sink and source inputs?
Current flows into a sink input from outside, and it works with a PNP-output sensor; a source input supplies current outwards and works with an NPN-output sensor.