Allen-Bradley 1771-VHSC Very High-speed Counter Module

Overview

Chapter Objectives: This chapter provides information on the following aspects of the VHSC module:

• Features of the VHSC module
• Communication with programmable controllers
• Module operation

The 1771-VHSC Counter Module is designed for high-speed counting in industrial applications. It is an intelligent block transfer I/O module that interfaces signals with any Allen-Bradley programmable controller capable of block transfer. Block transfer programming moves module status data from the module’s memory to a designated area in the processor data table and transfers configuration words from the processor data table to the module memory.

Module Description

The VHSC module is a single-slot module that does not require an external power supply (note that the outputs do require a power supply). After scanning the inputs and updating the outputs, the input data is converted to a specified data type in digital format for transfer to the processor’s data table upon request. Command and configuration data are sent from the programmable controller data table to the module using a Block Transfer Write (BTW) instruction.

Features of the Module

The VHSC module is capable of counting pulses from various sources such as encoders (e.g., Allen-Bradley Bulletin 845H, K, F, P, E, and L), pulse generators, mechanical limit switches, and proximity switches. It returns the count or frequency in either binary or BCD format.

Key features of the VHSC module include:

• 4 Input Channels: Configurable for encoder mode, counter mode, period/rate mode, and continuous/rate mode.
• 8 Outputs: Isolated in groups of 2, with outputs current-sourcing at 5 to 24V DC (2A maximum per output).
• Inputs: Supports single-ended or differential inputs.
• Encoder Inputs: 2-phase encoder inputs up to a frequency of 250KHz.
• Counter Inputs: Single-phase counter inputs up to a frequency of 1MHz.
• Input Voltage Range: 5 to 24V DC.
• Status Return: Returns either count or frequency in binary or BCD format.
• High Input Counts: Supports input counts as high as 999,999.
• Frequency Modes: Supports up to 500KHz in period/rate or rate measurement frequency modes.
• Output Flexibility: Outputs can be tied to any counter, with each output having a user-selectable on-off value, and can be tied back to an input for cascading.
• Automatic Configuration: Features automatic default configuration.
• User-Selectable Values: Each counter has a user-selectable preset and rollover value.
• Totalization: Supports period/rate with periodic outputs and period/rate with dynamic outputs for totalization.

Operating Modes

The 1771-VHSC module operates in the following modes:

• Counter Mode
• Encoder X1 Mode
• Encoder X4 Mode
• Period/Rate Mode
• Rate Measurement Frequency Mode
• Continuous/Rate Mode

Each mode's operation is specifically tailored to meet the requirements of different counting and measuring applications in industrial environments.