Temperature transmitter calculations

Q&A Temperature

Our temperature transmitter has an input range of 0 to 100 degrees Celsius, an output range of 4-20 milliamps, and accuracy of ±0.5 percent. If the output of the transmitter is 13.6, what are the ideal minimum and maximum temperatures? I calculated between 67.5 and 68.5. Am I right?

Expert’s answer: Temperature transmitter calculations

Nice try, but the resolution is simpler than your answer. So let’s organize and give you a clear step by step to make sense of your temperature transmitter calculations. First, we’ll start with your specs.

Transmitter range: 0 – 100°C

Output range: 4-20 mA

Accuracy: ±0.5%

Now the output is 13.6 mA, and you want the process values, right? So here we go.

  • PV – LRV / SPAN = mA – LRV/SPAN
  • PV – 0/100 = 13.6 – 4/16

Still with me? Good! Let’s keep breaking it down.

  • PV – 0/100 = 0.6
  • PV – 0 = 0.6 x 100

And finally, PV = 60°C!

  • LRV = Low range value
  • SPAN =  Device range from minimum to maximum
  • PV = Process value

So based on the 60 degrees Celsius, you can consider the accuracy ±0.5 percent. Keep in mind that to calculate accuracy you have to consider a lot of details, such as the resolution, sensitivity, gain error, linearity error, and more. Hope that helps!

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