Follow these five steps to prevent tampering and ensure effective and correct process adjustments for pneumatic components.
Steve Bain, Industry Segment Manager – Food and Beverage, Festo North America
In modern automation systems, the need for frequent process adjustments poses the risk of unwanted device tampering, often referred to in exasperation by plant managers as Unnecessary Knob Twisting (UKT). UKTs result when operators believe they know their machine’s operation better than anyone else and fiddle with a process to make the machine run more smoothly. There are entire Total Productive Maintenance (TPM) programs dedicated to monitoring adjustment points principally due not only to UKTs but also to machines not in optimum condition. Having a consistent machine is a dream for factory managers.
To address this issue and ensure efficient, error-free process adjustments for pneumatic components, plant operations departments can follow a set of five essential steps. These steps include eliminating unnecessary adjustments, leveraging automation to reduce human error, implementing sensors for condition monitoring, maintaining centerlining, and using visual indicators.
Why is tamper resistance important?
OEMs are increasingly designing automated systems to run various product sizes and configurations. Frequent electric and pneumatic process adjustments become necessary in these systems. Changes in pneumatic adjustments are used to regulate flow, pressure, end-stop limits, and machine speed, among other variables. This ongoing need for adjustments, however, opens the door to unwanted device tampering, which can lead to machine malfunctions and process disruptions. The potential for safety risk certainly is also possible, especially if the UKT overlooked the root cause of the problem. There are many instances where a technician flew halfway across the country to diagnose a major problem causing downtime and lost production only to find a flow control valve — that had been perfectly set — had undergone a UKT.
An example of a tamper proof pneumatic system. All images courtesy of Festo
Step 1: Eliminate unnecessary process adjustments
The initial step towards efficient process adjustments involves identifying and eliminating adjustments that are unnecessary. The first of these is proper dimensioning during machine design. Using correctly sized components minimizes the need for pressure regulators or flow controls to adjust actuator speed or force. There has always been a tendency in pneumatics to oversize components to ensure enough flow and force. Don’t do it. Use engineering tools to properly size the components. Using smaller tubing, for example, may eliminate the need for flow control.
Use fixed-orifice flow controls. By embedding fixed-diameter orifices into valve manifolds, actuator speeds can be permanently set, eliminating the need for further process adjustments. Employ modular valve manifolds with multiple valve sizes. This strategy enables optimization based on specific applications, reducing reliance on flow controls.
Pneumatic cylinders equipped with automatic, self-adjusting cushioning features ensure optimal performance without the need for adjustment screws. There are regulators that can be locked in position. Once set, these regulators prevent unauthorized adjustments.
Self-adjusting pneumatic cylinders from Festo
Another advantageous outcome of eliminating adjustment points is that most components can be smaller and there are fewer of them. This translates into reduced upfront cost. Eliminating adjustment points also reduces maintenance costs as replacing an actuator will not require multiple manual cycles to establish proper flow control and cushioning settings.
Step 2: Use automation to eliminate human error
To minimize the potential for human error, selecting components with built-in automation capabilities is crucial. Use electric control where possible. One example is proportional pressure regulators that automatically adjust output pressure based on signals from a programmable logic controller (PLC). Additionally, advanced electric or servo-pneumatic actuators allow precise configuration of speed and force without pressure regulators or flow controls.
The Festo intelligent valve terminal VTEM showing the packaging of communication, processing power, sensors and pneumatic valves
Intelligent valve terminals combine pneumatics and electronics in a single package. These solutions enable digital control and analysis of valve function, flow rate, pressure, and other process parameters. For air flow control, these systems can integrate flow control valves on actuators and provide tamper-proof travel speeds. Furthermore, they allow the implementation of dynamic flow control, energy optimization, and leakage detection.
Step 3: Implement sensors for condition monitoring
To ensure the integrity of processes affected by adjustments, implementing sensors for condition monitoring is vital. Start by identifying monitoring opportunities, add sensing (with IO-Link this could not be simpler), and potentially gain the capability to determine when process variables are out of your control. Attributes like supply air pressure, humidity levels and vibration monitoring are candidates.
Pressure regulator locked and tamper proofed
Other areas to consider include differential pressure monitoring for filter replacements. Pressure sensors and switches that communicate with the PLC can verify automatically whether a process operates within the desired pressure range. Flow sensors are essential for monitoring the amount of consumed air and knowing whether the process is performing as expected.
Step 4: Maintain centerlining
Centerlining is a methodology that focuses on using established process settings to ensure consistent line operations. It works to decrease product and procedure inconsistencies by optimizing machine effectiveness.
A packaging machine may have mounted rulers at each adjustment point to determine where some component needs to be aligned. Additionally, manufacturers can use counters on rotary knobs for the operator to dial in the exact number where the setting should be at a particular time. To ensure consistency, use numerical scales for manual adjustments and seek out flow control components with position markings or digital flow meters.
Step 5: Take advantage of red and green visual indicators
For adjustment points that are not cost-effective to eliminate or automate, opt for pneumatic components equipped with red/green indicators. These offer a quick way to validate whether processes are performing as expected. Adjustable red and green ranges provide an extra level of safety for monitoring compressed air usage, allowing immediate identification of pressure within or outside the permitted tolerance range.
The vibrant and adjustable red/green zone dial face provides a visual cue when a system is out of range.
There are air filtration components, including pressure regulators and flow sensors, that feature scales with red/green ranges. Some flow sensors even use illuminating displays that turn red to indicate when the flow is beyond the desired range.
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