How to Test a 4-20mA Signal the WRONG WAY!
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- čas přidán 11. 02. 2024
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Honest question, is this not taught in school in the US? This is definitely taught in 1st year up here for instrument tradesmen.
I would say a good instrument class would teach this but not everybody goes through instrumentation classes
@@TimWilborne "Instrumentation Technician" is its own 4 year trade in Alberta, just like an electrician or gas fitter or carpenter. I get the feeling that a lot of states have quite varied requirements to become a tradesman. A very high percentage of programmers up here are qualified instrumentation techs.
It varies tremendously by location and industry.
Typically an analog input that is using a 4-20 ma signal should have a resistor.... Say 4-20 ma could be a 500 ohm resistor meaning you would expect to see 2 volts at 4 ma and 10 volts at 20... If you supplied 24 volts, you would see 48 ma. I would think the issue would come from a short, to ground or common causing the issue.
You also increase the wattage when you go above the needed voltage for 20mA. With your example
P = V^2/R = 24*24/500 = 1.152 watt (W)
A LOT of resistors are not good for 1 watt.