Using Siemens S7-1200 PLC with Incremental Encoders

Overview

• Discussed how to use Siemens S7-1200 PLC to read sensors and incremental encoders.
• Application contexts include packaging machines, conveyors, speed measurement, and distance measurement.

Types of Sensors

• Regular Sensors: Detect physical parameters like position or speed. Example: a roller with 100 pulses per revolution.
• Incremental Encoders: Provide higher resolution; e.g., 1,000 lines represent one revolution, yielding 1,000 counts per revolution.

Key Concepts

• Count and Speed Measurement:
  • Use high-speed counters to read counts from channels (e.g., ID 1000).
  • Counts can be translated to Revolutions Per Second (RPS) or Revolutions Per Minute (RPM).
• Incremental Encoder Basics:
  • Typically outputs two channels (A and B).
  • Direction of rotation can be determined by comparing A and B signals.
  • Can be set up for quadrature output, counting four times per pulse for increased resolution.

Configuration Steps in TIA Portal

1. Controller Setup:

   • Using S7-1200, e.g., CPU 1211 with high-speed counter resources.
   • Up to 6 high-speed counters available, capable of handling up to 100 kHz.

2. High-Speed Counter (HSC) Configuration:

   • Select the counter mode (e.g., counting mode).
   • Use A-B counting for directional sensing.
   • Set initial counter values and limit values.

3. Event Configuration:

   • Reference value setting allows outputs to trigger based on counters reaching defined thresholds.
   • Hardware interrupts can be set to execute upon reaching certain counter values.

4. Input Filtering:

   • Set the input filter time according to the encoder’s frequency capabilities.
   • Recommended to set below 0.8 microseconds for 100 kHz.

Programming Logic

• Counter Reading:
  • Use program blocks to read and assign counter values to internal variables.
  • Example: Move count from channel ID 1000 to an internal memory variable.
• Direction Control:
  • Use count up/down configurations through CPU properties, not through the program.
• Count Initialization:
  • Use function blocks to set preset values for the counter, useful for retaining values across reboots.

Practical Application

• Demonstrated setting up a basic system where:
  • An incremental encoder mounted on a motor shaft is read by the PLC.
  • The motor is run at known speeds to verify counter readings.

Conclusion

• This application showcases the fundamental principles of using a Siemens S7-1200 PLC with incremental encoders.
• Next video will cover translating counter readings to speed calculations for practical applications.