The formula for calculating equivalent current (ma) from known process variable (PV), Lower range value (LRV) and Upper range value (URV).

## Formula to calculate mA from PV

##### The formula is:

SPAN = URV – LRV

Where

PV Â Â Â Â Â = Â Process Variable

LRV Â Â Â = Â Low Range Value

URV Â Â Â = Upper Range Value

maÂ Â Â Â = milli ampere

Consider left side of formula for Process variable, LRV of transmitter lower range, Span is the difference between LRV & URV of transmitter ranges.

Consider right side of formula for current (ma), LRV of standard current range .i.e is 4ma,

Span is the difference between LRV (4ma) & URV (20ma) of standard current range

.i.e. 20 – 4 = 16, Using this formula we can calculate ma from pv and as well as pv from ma.

#### For example: The temperatureÂ transmitter range is 0 to 50 deg c andÂ Â known current ma is 12 then how to calculate the PV of the transmitter ?

Known values :

LRV = Â 0

URV = Â 50

mA = 12mA

Standard mA LRV and URV values are as follows –

LRV = 4mA

URV = 20mA

Span = URV – LRV

Span = 20 – 4

Span = 16

Required :

PV = ?

Formula :

##### Â Solution:

Put Values in Formula

__PV â€“ 0__Â =Â

__mA â€“ 4Â__

SPAN Â Â Â Â Â Â Â Â 16

SPAN = URV – LRV

SPAN = 50 – 0

SPAN = 50

PV – 0Â = Â Â Â Â 0.5 Â * 50

PVÂ = Â Â Â Â 0.5 Â * 50

PVÂ Â = Â Â 25

**Also Read:Â Instrumentation Formulas**

## 6 comments

Good

Dear bhardwaj sir,we have Polmon system.we controlling temp and rh in are bye it system. Now there temp showing wrong when getting 13 mA .but system range is -40 to +60 degree .how many should be there PV temp.

We calculate PV from mA through u given formula mA convertor .bt temp value getting wrong.plz give me rply.

For formula to calculate PV from mA. Click Here

Explain in detail

outstanding

plz transmitter calibration step by step full process