Instrument Validation – Tips and Tricks for Process Measurements


I think it’s human nature to want to mistrust equipment when we aren’t getting the results we expect. Inline analyzers are fantastic and can give us great real-time results, but when the readings aren’t what we think they should be, our instinct is to grab a roll of black electrical tape and cover up the display. I even find doubt creeping into my thoughts when I’m using recently calibrated instruments to help customers troubleshoot issues in their breweries. That’s why it’s great to have a way to validate an instrument that gives us confidence in our results.

The easiest way to validate an inline analyzer is to use your preferred portable or lab analyzer to double-check your readings. But that means you need to have confidence in your portable analyzer too. Here are a few tips on how to validate your verifying instrument, and then where to measure in your process when you’re ready to double-check your inline instrument. You should be able to apply these ideas not only to dissolved oxygen measurements, but to other types of parameters too.

  1. Start be making sure your validation instrument is really working properly. Check it against some old beer whose values you already know. If it’s reading as expected, you’re probably good-to-go, but if you want to validate it more, try measuring more than one thing, like a source of beer with higher values.
  2. To then use your portable to check your inline sensor, the best validation point is after the inline, but as close to it as possible. It helps if this measurement point is off a process pipe and not in a beer vessel, because it’s possible to see values go up or down in beer tanks. The readings can go up if there is air in the tank and down if the tank is well flushed with CO2 and the fill is turbulent.
  3. Once you’ve validated your inline readings and are confident it’s not an instrumentation issue, then to find the source of your dissolved gas problem you move to the nearest sample point before your inline instrument and move backwards in the process, measuring in as many places as you have sample valves. Using this method, you should be able to pinpoint the origin of any gas ingress, but if this doesn’t yield results then try slowing down your beer flow in the process pipe. If you can lower the flow and not increase the pack pressure in the pipe, it will lessen the venturi effect and help pinpoint culprits like leaky pump seals, valves, or fittings. All of these things can contribute to gas ingress, especially in pumps that work too hard at the end of a filtration run and centrifuge seals as they get warm.
  4. If you do find there’s a problem with your inline analyzer, then it may be time for maintenance. Optical sensors drift up over time, while electrochemical sensors drift down, and some CIP (Cleaning in Process) protocols can also phase-shift an optical sensor, giving a false high reading. Also, if your in-line optical sensor is reading high, it’s possible your zero calibration gas contained some oxygen and the instrument was improperly calibrated. Likewise, if your inline EC sensor is reading low, then it probably needs maintenance or cleaning.

My final thought for today is to not wait for high or low readings, but to validate on a regular basis. You’ll gain confidence in your instrumentation and have better control over your entire process.

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