Instrumentation
Analog Raw Counts to Engineering Units
Convert between the raw integer an analog input card reports and the engineering value, in either direction, with the resolution per count.
Results
- Raw count
- 16,384.0
- Engineering value
- 12.5004ft
- Percent of span
- 50.00%
- Equivalent current
- 12.0002mA
- Resolution per count
- 0.0007630ft
- Within the configured range
- Yes
The smallest change the card can represent. Filtering below this is meaningless.
The arithmetic
- EU = ((16,384 - 0) / 32,767) x 25.000 + 0.000
- EU = 12.5004 ft
What this does not account for
- There is no universal raw count range. Read it from the module manual, then confirm it by injecting 4 mA and 20 mA and observing the value online.
- If the channel is configured for 0-20 mA but the loop is a 4-20 mA transmitter, the reading is 25% high at zero and the error shrinks toward full scale, which looks like calibration drift rather than a configuration error.
- Clamp the scaled result and flag out-of-range raw values separately. Without clamping, a fault current produces a physically impossible engineering value that downstream logic will act on.
How this is calculated
Scaling a raw analog count to engineering units is a linear map: subtract the count at 4 mA, divide by the count span, multiply by the engineering span, and add the lower range value. The raw count range is specific to the module and must be read from its manual, then confirmed by injecting a known current.
Formulas
EU = ((Raw - Raw_min) / (Raw_max - Raw_min)) x (EU_max - EU_min) + EU_min
Assumptions built into this calculator
- Linear analog input with the endpoints you enter.
- Does not model card accuracy, linearity error, or drift.
Frequently asked questions
- What raw value corresponds to 4 mA on my card?
- It depends entirely on the module and its configuration. Read the manual and then verify by injection. Assuming a value is the most common cause of a scaling error.
Direct contact
Have a controls question?
Reach Eric Sullivan directly about anything on this site, a controls or automation topic, or one of his personal projects.