Omega-vehicle-security freedom OM-550 Manuel d'utilisateur télécharger pdf (Page 42)

OM-550 u37u

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.

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Omega-vehicle-security freedom OM-550 Manuel d'utilisateur Page 42