The accuracy specified by ASME under B40.1 standards fall under 8 different “grades” to help describe a pressure instrument’s true level of ability to read accurately. Below are the different grades and their corresponding accuracies.
Grade 4A = 0.1% full scale
Grade 3A = 0.25% full scale
Grade 2A = 0.5% full scale
Grade 1A = 1.0% full scale
Grade A = 2-1-2% – 2% accuracy on first 1/4 of the scale, 1% on the middle 1/2, and 2% on the last 1/4 of the scale
Grade B = 3-2-3% – 3% accuracy on first 1/4 of the scale, 2% on the middle 1/2, and 3% on the last 1/4 of the scale
Grade C = 4-3-4% – 4% accuracy on first 1/4 of the scale, 3% on the middle 1/2, and 4% on the last 1/4 of the scale
Grade D = 5% full scale
Accuracy of the pressure, temperature, flow, or level instrument you’re reading is obviously important. Otherwise, how would you know if the reading you’re seeing is reliable or not?
For simplicity, we’ll go over a couple common scenarios. The first and easiest one to calculate is Full Scale accuracy. So, for example, if you have a pressure transducer that reads 0-200 psi and the accuracy is 1.0% FS (or Full Scale), that means the reading your transducer is sending out is +/- 1% of the full scale of the sensor. So, in this case it would be +/- 2 psi. If your transducer was showing a reading of 56 psi, then the “true” pressure could be anywhere between 54-58 psi (or +/- 2 psi from 56 psi).
Another common accuracy you may see on a pressure gauge would be a 2-1-2% or 3-2-3% accuracy. So, in the case of 3-2-3%, what this means is that on the first 1/3 of the scale the accuracy is +/- 3%, the middle 1/3 is +/- 2%, and the final 1/3 is +/- 3% accuracy.
If you’re concerned about the reading of your sensor, please give us a call or email. We’d be happy to answer further questions.
As odd as it might seem to see a gauge filled with an odd thick liquid, it’s actually quite common. The liquid in the gauge (usually glycerin) acts as a dampener during high vibration. Because a pressure gauge has many mechanical parts as well as a sensitive pointer, vibration on a gauge would cause the needle to shake back and forth making it difficult to read the pressure as well as cause the gauge a lot of wear and tear. Read this Blog Post on gauge options for vibrating application for more information.
The most common fill fluid for a gauge is Glycerin. Some other fill fluids could include Silicone, Glycerin/Water Mix, & Halocarbon.
Not much. They’re often used interchangeably in the pressure sensing world. If you’re getting specific, a transmitter usually refers to a sensor with a current signal such as 4/20mA and a transducer usually refers to a sensor with a voltage signal such as 0-10VDC or 1-5VDC
Proof pressure is the pressure the unit can handle over its nominal range without affecting its performance or accuracy.
Burst pressure is the pressure the unit can handle over its nominal range before it leaks, ruptures, or explodes into teeny tiny little pieces all over your facility.
Please note that for proof pressure, while the instrument shouldn’t break, consistently subjecting an instrument to its proof pressure will eventually damage it or make it fall out of calibration much quicker. Proof pressure is meant as a guideline for a once-in-a-long-while scenario. If you find yourself getting up to the proof pressure often, then you should look into a higher range sensor.
Big Bear Instruments offers products from a wide variety of manufacturers including Ashcroft, Anfield, Eagle Signal, Gems, Harwil, Knick Interface, Kodiak Controls, Noshok, Plast-o-matic, SSI Technologies, Tel-Tru, Weksler Glass Thermometer Corp, and West Control Solutions. Please see our Manufacturers page for a full list of companies that we represent.
Not a problem. Through Big Bear's relationships with multiple manufacturers and distributors, our warehousing capabilities, and general industrial knowledge, there is no limit to what we can provide our customers.
Look no further. Big Bear Instruments is a full supporter of “Buy American” which is why we offer a full line of instrumentation and valves that are made or assembled here in the U.S.A.
You bet. We can apply a diaphram seal and capillary fill for both standard and specialty applications.
Absolutely. Big Bear Instruments can provide your custom dial pressure gauge with special ranges/scales, private labeling, custom logos, and unique colors. Visit our custom dials & private labeling page for more information.
We offer expedited 1-day turnaround for NIST certification of pressure instruments.
Short answer – Any. If you’re looking private label your sensing instrumentation or valves, then Big Bear can do it. For pressure gauges or thermometers, we can customize dials to show your company’s logo. For other instrumentation like sensors, switches, valves, etc, we can customize the labels we put on the instruments to show your company’s name or logo as well as any specific part numbers you want to use.
Big Bear Instruments has the ability and means to design and produce customized instrumentation, fittings, or valves to fit a customer’s specific application and/or need. Just contact us and a technical specialist can work with you to make what you need.
Yes. If you have a pressure gauge, transducer, valve, switch, or any other instrument that’s going to be used with oxygen, it’s vital to get the instrument cleaned for O2 service to remove any potential oils or contaminants. We can certainly do this. Make sure when inquiring to us about the instrument that you mention it’s going to be used on oxygen service and will need to be cleaned.