Brewery Inline Sensor Placement: Validation Techniques


My last couples of posts have dealt with sensor validation. I recently did some coaching on inline oxygen sensor placement, so I’d like to continue that discussion with those examples. One placement was pre-and-post centrifuge in a regional brewery and the other was in a process pipe flowing at about 500 gallons-per-minute. While the flow rate may make a difference in how far a sensor needs to be from pumps and other interferences, the same techniques can still be used to determine sensor placement.

The key to great dissolved gas measurement is making sure to measure in places where all of the gas is in solution. The same validation tips used for double-checking instrumentation can help you decide where to place an inline analyzer. In general we can say that if you measure close to a known – or at least probable — source of air ingress and yet can’t detect the full impact, but measure farther down the process and find higher values, then you probably want to place your sensor further away from that source.

Let’s talk first about the pre-centrifuge application. Since a centrifuge creates a small amount of vacuum, I don’t recommend putting a sensor immediately before it. Where there is any type of a vacuum, there is the possibility of a false low reading, especially if the vacuum can cause any foaming or bubbles forming in the beer due to degassing. If possible, I’d place a sensor where I’m fairly sure there is no suction on the beer.

You can get a false low reading post centrifuge as well, but for different reasons. The first is that any dO2 that ingresses via the centrifuge may not be fully dissolved in the beer in a short run to a sensor. The second is that any CO2 forced out of solution in the centrifuge may lower the dissolved O2. (The CO2 will carry O2 out with it, but then they will both reabsorb farther down the line.) In both cases, you can do better by placing the sensor at a distance post centrifuge.

Validation of inline sensor placement is easy if you use a portable instrument to help, even if you are measuring over a long distance. First take readings with both the inline and the portable at the farthest reasonable sample port from your Bright Beer Tank. If you get similar readings on both, you’ll know that your inline is correct and that you can trust both instruments. Then use your portable to take another sample at a port just before your bright beer tank. If there is more dO2 than you found at your inline placement, then you may have an ingress problem that needs correcting. (You may be tempted to test right in your BBT, but don’t. Tank filling nearly always results in pickup or loss of DO2, so measuring for that variable is a whole different matter.)

The advice I gave to the customer who was evaluating the 500 gallons-per-minute process pipe was similar, and can likewise be applied to most placement situations. Here’s a summary of my basic guidelines for the best inline probe locations:

–        As far as possible from the outlet of pumps

–        At least five pipe diameters from bends

–        As far as possible from CO2 or O2 injection

–        Never in a descending pipe

My final thought is to always validate an inline sensor location if possible. Remember to look for the places in your process where all of the gas in your beer is in solution: that’s usually the best place to put a sensor.


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.

Frivolous Friday – More on Old Beer Cans and Church-keys


I had the honor of speaking at my local MBAA chapter’s quarterly last night. While we socialized and sampled a great variety of beer, I noticed that someone had put out a large box of churchkeys for bottle opening. This was the biggest supply of that traditional, long-forgotten opener I’ve seen since I was a kid, and it reminded me of this photo sent by my friend Abe. Thanks to Lars, Jeff, Brian and the rest for inviting me to talk last night.


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