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User Guide
This measurement to 4 to 20mA sqrt extraction converter tool will convert any linear measurement reading to the ideal current loop signal over a non-linear square root extraction scale of 4 to 20 milliamps. This is useful for measurement devices where one measurand is proportional to the square root of another measurand, e.g. flow through a pipe is proportional to the square root of the differential pressure. A square root extraction 4-20mA conversion scale is also displayed for each selected measurement range.
Formula
This tool uses the following formula to calculate the current output signal over a square root extraction 4-20mA range from a specified linear measurement input reading and range:
SqRt mA out = 4 + (16 x √ ((Rdg – Low Limit) / (High Limit – Low Limit)))
Parameters
Measurement Unit
Enter the measurement unit associated with the input values.
Linear Measurement Reading
Add the measurement value you wish to convert from, in any engineering units. Please use a value which relates to the same engineering units as used for the “Lowest” and “Highest” values.
Lowest Linear Measurement
Enter the lowest range value for the measurement instrument you are converting, for most application s this will be zero. Please use a value which relates to the same engineering units as used for the “Reading” and “Highest” values.
Highest Linear Measurement
Input the highest range value for the measurement equipment you are converting, which is typically described as the full range or full scale. Please use a value which relates to the same engineering units as used for the “Reading” and “Lowest” values.
Square Root Extraction Signal (4-20mA) – Answer
This is the 4-20mA square root extraction signal that you would expect excluding any errors contributed by the measurement instrument. The result given is displayed in milliamps (mA) relative to a non-linear 4 to 20 mA sqrt extraction signal scaling.
Help
Conversion precision
How precise is the conversion to sq rt 4-20mA?
The square root extraction 4 to 20 mA signal “Answer” is displayed to a precision of 9 significant figures.
Rangeable instrument
What do I use for the highest range value if I am using a rangeable instrument?
Use the highest value of re-scaled range rather than the nominal base range.
Input or Output
Does the sqrt 4-20mA signal represent an input or an output signal?
It can be either, for example you could use it to convert the pressure input to a dp pressure transmitter to determine the perfect square root output expected or you could use it to determine the expected measurement if your device is accepting a sqrt current loop input and converting it back to a linear scaled value.
4-20mA to 4-20mA
Can I use this square root converter to convert a linear 4-20mA signal to a sqrt 4-20mA signal?
Yes, just specify 4 for the “Lowest” value and 20 for the “Highest” value and the linear milliamp measurement you wish to convert as the “Reading”.
Percent scaling
Is it possible to use percent of full scale (%FS) rather than measurement units to input a reading?
Yes, any scale can be used as long as it is linear one. So for percentages you would enter zero for the “Lowest” value and 100 for the “Highest” value.
0 to 600 mmH2O to output conversion
What is the square root output over a 4 to 20 mA signal scale for a linear pressure range of 0 to 600 mmH2O?
Formula for linear %FS to SqRt 4-20mA
How to convert a percentage to ma in a square root flow transmitter, please show me a simple formula?
Please use the following formula to convert a linear reading expressed as a percentage of full scale:
[SqRt Output (mA)] = 4 + √([Linear Reading (%FS)] x 256/100)
