Omega Vehicle Security freedom OM-550 - Manual (Page 39)

OM-550 u 34 u
4.14.4 DATA SCALING (mX + b calculation)
The output voltage of a properly matched transducer can be read the but the data will
be in "volts" and the user might prefer data in units that reflect the application.
Programming the OM-550 to produce data in terms of the actual parameter being
measured is called Scaling.
The linear slope-intercept formula (Y = mX + b) makes this possible. Given an input
"X", careful choice of m and b can scale the output "Y" to any value, with some
restrictions:
•
Some m or b values will produce values too large (or small) to print, although
they will be correctly saved to memory for transfer to a PC. Such values will print
as "******". Refer to section 4.2 PRINT FORMATTING.
•
The OM-550 can resolve 100 µV (±0.0001 VDC). This means that one A/D
converter "count" (the LSB) is worth 0.0001 VDC and the maximum input voltage
(±2.0000 VDC) represents ±20,000 A/D converter counts.
•
The m and b values you choose must be within the allowable ranges:
-9.99999 < m < +9.99999 -999999 < b < +999999
The following equations show how to scale data to the actual value of the parameter
being measuring. They assume that an increasing transducer output indicates an
increasing parameter. (If your system is inversely proportional, just change the sign of
the m value). Remember that m and b can be positive or negative.
X1 = minimum voltage expected at the input
X2 = maximum voltage expected at the input
Y1 = minimum parameter value for your application
Y2 = maximum parameter value for your application
m = (Y1-Y2) / (X1-X2) b = Y2 - (m * X2)