Industrial Pneumatics & Pick-and-Place Integration Course

Preparing a PLC Program to Measure Costly Compressed Air Leaks

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To accurately analyze the financial impact of compressed air leaks, a system must first be configured to capture precise, repeatable baseline data.

This lesson covers how to isolate auxiliary equipment in the PLC, configure a physical flow meter to accumulate total volume, and program a cycle-count cutoff to ensure a controlled testing environment.

1. Program Modification and Actuator Isolation

Before establishing an energy baseline, components that could distort the data or disrupt the sequence must be bypassed. In this setup, an electric servo actuator from a previous project is isolated using specific ladder logic modifications:

  • Bypassing Sequence Steps: Parallel branches are placed around the position-complete bits (on Rung 0, Rung 4, and Rung 9) of the main sequence. This allows the program to advance through the steps without waiting for physical feedback from the electric actuator.

  • Disabling the Servo: An Always False Instruction (AFI) is inserted at the beginning of the servo activation rung. The AFI ensures the rung evaluates as false without deleting the logic or disabling the routine, preventing the servo from turning on.

  • Interlock Modification: To allow the machine to enter auto mode without the electric actuator present, any conflicting comparison instructions in the main routine are bypassed with a parallel branch.

2. Configuring the Flow Meter for Volume Accumulation

Instantaneous flow shows the current rate of consumption, which fluctuates constantly during operation. Tracking total consumption requires switching the flow meter to a totalizer function that acts like an odometer.

  • Accessing Menu Options: Press and hold the center button on the flow meter for five seconds until the display enters the configuration menu, showing F0 and FLU.

  • Navigating to Parameters: Use the directional buttons to navigate to parameter F10.

  • Changing the Measurement Mode: The default setting is N5 (instantaneous flow). Change this setting to AC (accumulated value) using the left button, then press the center button until the numbers reappear. The meter will now track the total volume of air used over time.

3. Programming a Fixed Cycle Baseline

Measuring energy usage based purely on time is unreliable because air leaks can alter the operating speed of pneumatic components. To keep the test controlled, the data collection must be restricted to a strict number of mechanical cycles.

  • Adding the Counter: A Count Up (CTU) instruction, designated as a cycle counter, is added to the final step of the sequence logic (where step equals 80). The preset value is set to 10 cycles.

  • Automated Sequence Cutoff: A normally open contact referencing the counter Done bit (cycle_counter.DN) is added to unlatch the system's auto mode storage bit. This automatically stops the machine the moment the 10th cycle is completed.

  • Reset Circuitry: A Reset (RES) instruction is placed in parallel with or immediately following the shutdown logic, using the cycle_counter.DN bit to clear the accumulated count so the program is ready for subsequent test runs.

Knowledge Check Quiz

  1. Why must the electric actuator be bypassed using logic modifications like the AFI instruction for this specific exercise?
    Click to reveal answer

    The electric actuator is not being evaluated for energy efficiency in this lesson. Bypassing its sequence steps and using an Always False Instruction (AFI) prevents it from drawing power or stalling the program, allowing a clean baseline setup of the pneumatic system alone.

  2. What configuration change must be made to the hardware flow meter to prepare it for tracking baseline consumption?
    Click to reveal answer

    The flow meter must be switched from instantaneous flow mode (N5) to accumulated mode (AC) within parameter F10. This changes the device function from a speedometer-style rate indicator to an odometer-style totalizer.

  3. Why is a fixed cycle count used to establish the data collection baseline instead of a fixed time duration?
    Click to reveal answer

    Air leaks can alter the operating speed of a pneumatic system, causing it to cycle faster or slower. Tracking consumption over a fixed time period would skew the data, whereas tracking over a set number of cycles ensures identical physical work is performed during tests.

  4. Which PLC instruction is programmed at the end of the sequence to track the operational cycles?
    Click to reveal answer

    A Count Up (CTU) counter is placed on the final step of the sequence (step 80) with a preset value of 10 to monitor the exact number of completed operations.

  5. How does the PLC program automatically halt operation when the target baseline cycles are reached?
    Click to reveal answer

    A contact driven by the counter's Done bit (.DN) is programmed to unlatch the system's auto mode bit. This drops the machine out of automatic operation the moment the preset count is achieved, while a Reset (RES) instruction clears the accumulator for the next run.