Most people who are selecting a vacuum gauge are not sure which one to use. Often, they have to spend time studying the manufacturer's product line to figure it out - who has time for that? If you know what kind of vacuum gauge you need for your work, this blog isn't for you. For anyone else, read on....
After several years of helping people find the proper vacuum instrument, we decided to outline these conversations to help others decide on the best tool for the job.
Here is what we find from customers:
- Although applications are widely varied, the basic questions are similar;
- Most people initially want the most accurate reading possible everywhere; and
- Most people settle for a gauge that covers the ranges that are important to them, versus paying much more for a complex solution that covers all the ranges with extreme accuracy.
So what's so hard about choosing a vacuum gauge?
The fact is that there are a lot of different vacuum gauges out there, and new ones are popping up every day. Is there one gauge that is better than all others? Compounding the first time buyer is the history of terminology that describes vacuum gauges, sensors, controllers and regulators. There are different technologies that dominate solutions depending on your vacuum region of interest. There are also several active gauges available that combine measurement technologies, but these aren't always the perfect fit either. The most important factor is what range is important. Knowing this and choosing the right technology will save you money and maintenance.
1. What pressure range are you looking for?
Many folks might say "the whole range." The whole useful vacuum range (perhaps from 1x10-13 Torr to 7.6x103 Torr) is addressable, but it is expensive. The real answer to this question has to do with the process that is being measured. Consider a coating process that goes down to 1x10-7 Torr to verify cleanliness, then sits at 80 millitorr for the coating, then backfills nitrogen until atmospheric pressure is reached. In this example the primary region of interest is 80 millitorr, but 1x10-7 Torr and atmosphere also need to be known. If it's not a dirty process, then a cold cathode Pirani combination might work well. If it is a dirty process, perhaps another solution. If the answer to this question is that 400 millitorr is the most important, and you need 10% accuracy.. where the difference between 360 millitorr and 440 millitorr matters, then the solution is more clear. Users typically care about a particular pressure or the base pressure of the system, and the other vacuum pressure points are for reference. Others care mostly about a pressure range. For example, users who work with altitude simulation might really care about the pressure at altitudes between 8000 and 80,000 feet, so that entire range is important.
2. What accuracy range are you seeking?
The key is to distinguish the accuracy level that matters to you. Typically, absolute vacuum sensor accuracy is expressed in % of reading. If a reading is 100 millitorr with an accuracy of +/- 10%, the actual pressure may be between 90 millitorr and 110 millitorr when the gauge reads 100 millitorr. The better the accuracy, or the tighter the range you are looking for, the more expensive the solution. In our Coating example, the primary range of interest was 80 millitorr and the acceptable range was +/- 10 millitorr, or a range of 70 millitorr - 90 millitorr would be acceptable.
3. Are there any other ranges that are important?
In the above Coating example, the nitrogen backfill reaching atmospheric pressure was important, along with knowing that 1x10-7 Torr was reached .
4. Do you need to control or regulate, in addition to measuring?
Sometimes customers just need to see the indicated vacuum pressure, and the rest is a manual process. Other customers have an elaborate, turnkey system filled with interlocks, and there are many variations of this. One of the most common requests is some sort of relay control that activates at a particular vacuum level, and an analog output to interface with a PLC or other system.
5. What form factor are you looking for?
In a laboratory, a desktop gauge usually works best. In a factory scenario, a panel mounted gauge often make more sense.
6. What kind of power do you need?
The two most common answers are 110VAC line power (for U.S.) or battery powered gauge for portable, field use.
In our Coating example, assuming that the user had a fairly clean process, and the gauge would be mounted away from the path of the target material flow, then an active gauge with a StrataVac controller probably makes sense.
If can answer these six questions, you're probably ready to select a gauge. Our product wizard asks you these questions, and then shows you the products that fit the criteria you select. Feel free to try it out!
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