The Importance of Periodic Calibration Checks for Proximity Systems

Most proximity systems are rugged and durable and provide very accurate results. Some manufacturers have advocated not checking the calibration of their proximity sensor systems. That could be because they have no way to perform a field calibration. Industrial plants are used to performing calibration checks and calibrating instrumentation, like temperature, pressure, flow, and level sensors annually. To never have to check the status of a key sensor seems abnormal, and it is. In API 670, version 5, page 29, it states that a user should be able to calibrate their proximity systems. Metrix recommends that you check the operation of your proximity systems, regardless of the manufacturer, at least every three years. If there is no way to calibrate the proximity system, be sure to check it before the warranty runs out, that way you can replace it if it does not meet specification. The Metrix Digital Proximity System (DPS) meets API 670 requirements and provides a means of calibrating the system, when necessary, even if you are using other manufacturer’s probes and cables.

Periodic calibration checks for your proximity vibration sensors and transmitters are the best insurance against faulty readings. Your predictive maintenance program hinges on the accuracy of your temperature, pressure, flow, level, and vibratory sensors. Not periodically checking your proximity sensors, as well as your casing vibration sensors, is a recipe for disaster. Unpredictable environmental factors and malfunctions can occur on-site. Calibration checks are a vital component of your safety protocols, ensuring that the facility meets both regulatory standards and its own standards. We’ll look at the function of calibration, tips on the best approach, and the consequences of overlooking the testing process.

The Importance of Instrument Calibration
Metrix offers a wide catalog of proximity vibration monitoring equipment, and each product plays a role in revealing the inner workings of a site’s processes and production. If a single bearing starts to become loose within a compressor, motor, generator, turbine, etc., a proximity sensor can relay this information back to the decision maker. Instead of having to make rough guesses about the production or maintenance schedules, people can devise more precise strategies in every situation. This enables them to continue to operate safely, while at the same time maintaining production.

However, despite the quality of our sensors and the larger system, they still require periodic calibration checks to ensure that the data being reported is accurate. This goes along with other manufacturers’ proximity systems. Regardless of the manufacturer, periodic checks at least every three years are necessary to ensure the proximity system is working properly. No matter what type of industry our equipment supports, whether it’s a separator in a food factory or a reciprocating compressor in a refinery, instrument calibration checks help everyone feel confident that they’re working off the most up-to-date numbers and measurements. The difference that Metrix makes is that our proximity measurement system can be calibrated if necessary. This is especially true when we use competitive probes and cables. We have hundreds of examples where our customer chose to keep the existing probe and cable and change out the driver or transmitter with a Metrix Digital Proximity System driver or transmitter to obtain an in-specification system.

Tips for Calibration Checks (Verification Tests)
Here are a few key points to keep in mind when devising a calibration checks schedule:

● Schedule: The minimum standard to perform calibration checks on proximity systems is at least every three years. In certain situations, a more frequent schedule may be required. Do not be talked into “You don’t need to check.” That will just lead to folly.
● Simulation: If the verification tests can’t mimic real-world conditions, the results won’t be of any real use to the plant. Calibration tests are only as good as the simulation provided. At Metrix, we like using the Hardy Shaker as a means of testing gap and vibration with a calibrated instrument. This way one can gap the probe to what they normally find in the machine, and they can vibrate the Shaker and obtain the peak-to-peak amplitude that they normally would encounter in the machine. One can then verify that the input signal from the shaker equals the output from the Metrix proximity driver or transmitter in the monitoring system or control system as appropriate.
● Documentation: All site staff know what it’s like to come across incomplete paperwork. Better labeling and reporting can make a major difference when it comes to your calibration procedures. Metrix understands this and has provided a report capability in the Digital Proximity System software. This allows a user doing calibration checks to easily create a report complete with all the necessary information and plots of the data, namely Incremental Scale Factor (ISF) and Deviation from Straight Line (DSL) Plots.
● Support: Products like mounting adapters and brackets can secure your proximity sensors, so that they’re less likely to be impacted by heavy vibrations. With rugged equipment and stable configurations, you're less likely to have compromised sensors. This can ensure that your calibrated equipment gets installed properly and provides lasting value.

If you set up a proximity sensor or system and then ignore it, the consequences can range from inconvenient to catastrophic. Instrumentation that’s only tested during machinery overhaul may provide outputs that are not indicative of the machine’s true condition. This is not to say that proximity sensors are faulty or otherwise unreliable, but more of a reminder that no device or product can ever be considered infallible. Metrix wants you to trust but verify, in order to keep you and your plant safe. The Metrix Digital Proximity System allows one to calibrate your proximity system to ensure it meets the requirements of API 670.

The Consequences of Improper Calibration
Calibration checks involve time and energy for the staff, not to mention costs for the facility. However, failure to perform thorough checks can result in the following consequences:

● Health hazards: The safety of site staff depends on the results of calibration tests. The more effort the organization puts into these checks, the more peace of mind they’ll have when their instrumentation is expected to work.
● Fines/profit loss: Compliance regulations come from a variety of sources, including insurance, state organizations, and federal governing bodies. If calibration checks aren’t regularly scheduled for your instrumentation, you may not be able to sell your products, or they might be subjected to a hefty fine, costly equipment failures, and unplanned downtime.
● False assumptions: Most site engineers and technicians are working with data that needs to be accurate, or else it will create a negative trickle-down effect and impact other decisions. The risks associated with inaccurate data include costly equipment failures and unplanned downtime, all of which can be avoided with calibration checks at least every three years. Remember, even with competitive proximity probes and cables, the Metrix Digital Proximity System can be used to calibrate those systems to ensure they meet the accuracy requirements of API 670.

The Metrix team has seen how valuable proximity monitoring equipment can be, particularly on sites where even a small shutdown could result in large operating losses. A routine of ongoing, thorough, calibration checks is the key to making the most of your instrumentation investment.