SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES

coefficient is 0.00385/°C. The change in nonlinearity of a PRT with the temperature coefficient of 0.00392/°C is minute compared with the slope change. Entering a slope correction factor of 0.00385/0.00392 = 0.98214 as the multiplier in Instruction 16 results in a calculated temperature which is well within the accuracy specifications of the PRT.

 

 

PROGRAM

01:

P6

Full Bridge

01:

1

Rep

02:21 2.5 mV 60 Hz rejection Range

03:

3

IN Chan

04:1 Excite all reps w/EXchan 1

05:

2500

mV Excitation

06:

11

Loc [:Rs/Ro ]

07:

0.001

Mult

08:.02344 Offset

02:P59 BR Transform Rf[X/(1-X)]

01:

1

Rep

02:

11

Loc [:Rs/Ro ]

03:

50

Multiplier (Rf) =R1/R0

03:

P16

Temperature RTD

01:

1

Rep

02:11 R/Ro Loc Rs/Ro

03:12 Loc [:TEMP C ]

04:.98214 Mult

05:

0

Offset

7.12PRESSURE TRANSDUCER - 4 WIRE FULL BRIDGE

This example describes a measurement made with a Druck PDCR 930 depth measurement pressure transducer. The pressure transducer was ordered for use with 5 volt positive or negative excitation and has a range of 5 psi or about 3.5 meters of water. The transducer is used to measure the depth of water in a stilling well.

Instruction 6, 4 Wire Full Bridge, is used to measure the pressure transducer. The high output of the semiconductor strain gage necessitates the use of the 25 mV input range. The sensor is calibrated by connecting it to the CR10 and using Instruction 6, an excitation voltage of 2500 mV, a multiplier of 1 and an offset of 0, noting the readings (*6 Mode) with 10 cm of water above the sensor and with 334.6 cm of water above the sensor. The output of Instruction 6 is 1000 Vs/Vx or millivolts per volt excitation. At 10 cm the reading is 0.19963 mV/V and at 334.6 cm the reading is 6.6485 mV/V. The multiplier to yield output in cm is:

(334.6 - 10)/(6.6485-.19963) =

50.334 cm/mV/V

The offset is determined after the pressure transducer is installed in the stilling well. The sensor is installed 65 cm below the water level at the time of installation. The depth of water at this time is determined to be 72.6 cm relative to the desired reference. When programmed with the multiplier determined above and an offset of 0, a reading of 65.12 is obtained. The offset for the actual measurements is thus determined to be 72.6 - 65.12 = 7.48 cm.

The lead length is approximately 10 feet, so there is no appreciable error due to lead wire resistance.

01:

P6

Full Bridge

01:

1

Rep

02:23 25 mV 60 Hz rejection Range

03:

1

IN Chan

04:1 Excite all reps w/EXchan 1

05:

2500

mV Excitation

06:

1

Loc [:HT cm ]

07:

50.334

Mult

08:

7.48

Offset

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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