a 4-20ma signal,500psi to 1250psi.at 7ma i was told you will get 640.625.whats the formula for this ratio thanks

4mA = 500 psi 20 mA = 1250 psi.
4-20 ma is the span 16 mA is the range
500 - 1250 psi is the span 750 is the range
7ma - 4mA = 3mA 3/16 is the % of range
3/16(750)= % of psi range = 140.625psi
Add the 140.625 to the minimumn span of 500 psi to get 640.625psi.

[(signal mA - 4) divided by 16] X (variable range) + variable minimum span

Don(resqcapt19)

Or...

750(engineering units span or range) divided by 16(signal span or range)= 46.875 PSI per mA.
3 x 46.875 = 140.625
140.625 + 500(zero value) = 640.625

conversely...
16 divided by 750 = .02133 Psi per mA
.02133 x 140.625 = 3mA
3mA + 4(live zero value)= 7mA