Intermediate Checks per ISO 17025 (aka “equipment verifications”) are an often-overlooked, but vitally important part of maintaining accurate measurements for manufacturers. This process can catch errors in your sensors and measurement devices before they become serious problems. An increasing number of companies are starting to catch on to the importance of performing intermediate checks, or verification of equipment, between calibrations, but many more still can reduce risk for their businesses by adopting procedures to perform intermediate checks. Whether you are maintaining temperature, pressure, or electrical devices, understanding and employing intermediate checks on your equipment in your manufacturing procedures could be the one of the best things you do for your business.
Intermediate Checks vs Calibration: What’s the Difference?
Calibration is the process of comparing a device to a measurement standard. Calibration will give you the “error” of your device or sensor, or how far it has drifted from its nominal value, be that a volt, ampere, or a degree of Celsius. The measurement standard itself has been calibrated by a more accurate standard, and this process is repeated until the calibrations are connected. The definition of the measurement unit itself is defined by the International System of units (SI). Fluke Calibration builds measurement standards of several different levels of accuracy to enable people to compare their devices to measurement standards. This is referred to as a calibration “traceable to the SI.” Through a well-defined calibration process in accordance with the international standard, ISO 17025, every device used in a calibration measurement can be traced back to the international standard units. The SI units are maintained by a network of National Metrology Institutes such as NIST, BIPM and many others. In summary, when you send a device to a calibration lab, they’ll first calibrate the device to understand how far off of nominal it is, and then do a verification that the device is performing in or out of the tolerance that is defined by the published specifications.
The next part—and commonly confused with calibration—is called adjustment. If a device is found to be performing outside of its published specifications, adjustment is the process of using information obtained during the calibration eliminating the errors, so that the device will measure much closer to its nominal value.
Calibration and alignment are performed on a time cycle, most often referred to as a calibration interval. The most common cycle for calibration is one year. However, it can be more or less depending on the requirements of that process.
That’s all well and good. But there’s a lingering question: If you only perform calibration and adjustment on an annual cycle, and the device comes back out of calibration, how can you trust the measurements you made with that device since the last time it was found in calibration? Calibration will not inform you at what point during that yearly cycle the device became out of calibration. Every measurement you’ve taken with that device since its last calibration is now suspect.
It goes without saying that in many industries, this can pose a huge risk. In heavily regulated industries, such as pharmaceuticals or food production, discovering that a device is out of calibration has the potential to become very costly. For example, if a sensor measuring temperature in a freezer is out of tolerance, everything that was stored in that freezer may have to be discarded or recalled. Manufacturing defects and equipment failures are possible if at any time in the last year, the devices used to test products on the factory floor were found to be out of tolerance. There is not only a financial risk, but for many products, human health can be jeopardized as well. The sooner you know when a device or sensor has become out of tolerance, the lower the risk and costs to your business will be.
The Solution is to Perform Intermediate Checks Between Calibrations
Intermediate Checks, or Verifications of Equipment, are measurements of devices in smaller increments of time than your calibration cycle, to verify that it’s still within the bounds of acceptable performance. While it’s typically performed in regulated industries such as pharmaceuticals and medical devices, in other industries it is much less common, especially when there is no regulatory body. Even in some regulated industries, such as aerospace, it’s less common because the FAA only begins its investigation into measurement devices when an aircraft component fails.
Because of the risk for part failures and recalls, I believe more industries will start to look at the importance of intermediate checks. The automotive industry is one example of an industry that is scrutinizing the quality of its components, particularly from vendors of parts and sensors, after experiencing headline-grabbing recalls in previous years. Grocery recalls are another example of the potential risk posed by inaccurate sensors. These potential problems are not just costly, but also capable of causing harm to humans. Manufacturing industries such as steel producers are other examples where accurate sensors and instruments can have serious repercussions on product integrity if they not been checked between calibrations. The practice of intermediate checks in those industries is reducing the risk of failures and financial loss, without the time and expense that increasing the frequency calibrations would incur.
In electrical device manufacturing, intermediate checks are becoming more recognized for its importance in new product lifecycle and performance testing. For example, a prototype air conditioner might be put through its paces in a laboratory, running it at extremes until it breaks. The engineers will be collecting data the entire time. Clearly, what you don’t want to have happen is, after running weeks of tests, you discover that the sensors collecting that data aren’t accurate. Verifying those sensors before and after the test is a sensible way to reduce the risk of errors in product development.
Suggested Equipment for Intermediate Checks
Temperature
9100S, 9102S Handheld Dry-Wells
9142, 9143 & 9144 Field Metrology Wells
4180 and 4181 Portable Infrared Calibrators
1523, 1524 Reference Thermometers
1551A Ex / 1552A Ex "Stik" Thermometer Readout
Pressure
3130 Portable Pressure Calibrator
P5510-2700G, P5513-2700G Pneumatic Pressure Calibrators
P5514-2700G, P5515-2700G Hydraulic Pressure Calibrators
700HPPK Pneumatic Test Pump Kit
Fluke 729 Automatic Pressure Calibrator
Electrical
5502A Multi-Product Calibrator
7526A Precision Process Calibrator
Tips for Incorporating Intermediate Checks into Your Calibration Process
My background is in automation and production for factories. Among the types of measurements for testing products as they are being manufactured, temperature is among the most common, but electrical and pressure measurement solutions are also readily available. If you’re not practicing intermediate checks in your environment, here are a few pointers to get you started.
- Consider portability requirements. When you adhere to a calibration cycle, typically this involves removing a sensor or shipping a device to the calibration lab. When you’re performing checks on equipment, you may not practically be able to remove the sensor; instead, you might need to perform intermediate checks at the site of the installation. I’ve seen some manufacturers design custom carts that can be wheeled around the factory floor, with all the equipment they need to test their sensors. Fluke Calibration makes a wide variety of field metrology wells and dry block calibrators that are portable and can perform intermediate equipment checks. For temperature checks, convenient handles and light weight make them easy and practical to carry around a factory floor. For pressure gauge checks, often the measurements will be taken on-site in open weather or precarious situations, making portability and ruggedness important factors.
- Determine what uncertainty budget works for you. What level of uncertainty is good enough in verification is a tough question to answer directly, but if you adhere to your calibration cycle, you might be able to settle for a 2:1 or even 1:1 uncertainty ratio rather than a 4:1 uncertainty ratio required for most calibrations. Some may opt for handheld dry wells or pumps designed as process calibrators, while others may opt to use a “gold standard” measurement device to check against the measurement devices they regularly put into use. Keep in mind that when using gold standard methods of comparing instruments, you can run the risk of both instruments being out of calibration. To mitigate this, some will use two gold standard devices when performing the intermediate check to reduce the risk of making a wrong decision from a gold standard drifting. (Remember to calibrate those gold standard devices regularly as well.)
- Look for changes in measurements between calibration. Calibration is an absolute measurement against a known standard, but intermediate checks may only need to look at changes between measurements. If sensors are drifting in comparison to the more stable measurement device you’re using to perform intermediate checks, that’s a red flag that there’s a problem and the device needs to be replaced or aligned. If you’ve noticed that there’s a problem with a device early on and addressed it, you’ve succeeded in reducing what could have been a much larger problem if left unnoticed.
Do you have a question about intermediate checks or calibration in a manufacturing environment? Give us a call at 877-355-3224, email me directly at jack.berlekamp@flukecal.com, or request a sales consultation. If you’d like to learn more about metrology, we offer online and in-person training, as well as free on-demand and live webinars on many calibration topics.