Omega Vehicle Security OM-550 manual Matching and Scaling a Current Transducer, Example

4.14.6 MATCHING AND SCALING A CURRENT TRANSDUCER

Example:

Given a 0 - 150-PSI transducer with a 4-20 mA output.

Program the OM-550 to indicate 0 - 150 PSI with 0.01-PSI resolution.

If the 4-20 mA Current Probe is being used, begin with step 2, below. (This probe is already matched to the OM-550).

1. First, find the Matching resistor:

R1 = 2 / I

=2 / 20 mA

=2 / 0.02

=100 Ω

When the transducer output is 4 mA, the OM-550 will see 0.4 VDC and when the transducer output is 20 mA, the OM-550 will see 2 VDC.

2. Next, find m & b:

X1	=	0.4000 VDC	ç minimum expected input
=	4000 A/D counts		at Transducer minimum output
X2	=	2.0000 VDC	ç maximum allowable input
=	20000 A/D counts		at Transducer maximum output
Y1	=	0.00 PSI	ç minimum transducer output
=	0.00 PSI		ç choose decimal point = 2

Y2 = 150.00 PSI

=15000 display counts

m= (Y1 - Y2) / (X1 - X2)

=(0 - 15000) / (4000 - 20000)

=0.93750

b = Y2 - (m * X2)

=15000 - (0.93750 * 20000)

=-003750

Notice the decision to indicate with 0.01-PSI resolution determined a decimal position of 2.

OM-550 u37u