Lab 3 Static Calibration of Electronic Pressure

Transmitters using Manometers

February 1, 2013

Group 0

Miles Greiner

Lab Instructors:

Michael Goodrick and Alyssa Hawthorne

Abstract• The purpose of this lab is to

– Calibrate an electronic pressure transmitter using an inclined-well monometer, and

– Interpret the manometer manufacturer’s accuracy specification. • The best estimate for the true pressure head in terms of the

transmitter reading is: – h = 1.015hT + 0.007 inch H2O, with a confidence interval of ST,M

= ± 0.010 inch-H2O (68%)– The maximum error in the reading is 0.062 inch H2O, which is

roughly equal to the manufacturer’s specification.• The manufacturer stated manometer uncertainty is 6 times

larger than the value of SM,T, corresponding to a nearly 100% confidence level.

• The manufacturer’s specified uncertainty is in the same order of magnitude of the error measures determined in this experiment.

Table 1 Equipment Specifications and Calibration

• The manometer is used to calibrate the transmitter because, after two years, the manometer’s uncertainty is smaller.

Number I3

Range 0-4 inch H20

Relative Accuracy ±1% FS

Absolute Accuracy ±0.04 inch H2O

Number T6

Range 0-3 inch H2O

Relative Accuracy ±0.25% FSStability 1% FS/year

Absolute Accuracy (after 2 years)

0.06 inch H2O

Tranfer function hT = (3 inch H2O)(IT-4mA)/(16mA)

Transmitter

Manometer

Table 2 Calibration Data

• This table shows one cycle of increasing and decrease pressure calibration data.

• The transmitter pressure head was determined from the measured current using the manufacture specified equation in Table 1

• The transmitter pressure head reading did not return to zero at the end of the descending cycle.

Manometer

Reading, hM

Transmitter

Current, IT

Transmitter

Reading hT

[inch-H2O] [mA] [in H20]

0 4 0.0000.4 6.03 0.3811 9.12 0.960

1.6 12.33 1.5622.4 16.6 2.3633 19.67 2.938

2.6 17.68 2.5651.8 13.47 1.7761.2 10.29 1.1790.6 7.09 0.5790 4.01 0.002

Fig. 1 Calibration Data and Linear Fit

• The transmitter reading is consistently lower than the manometer-indicated pressure.

• Standard errors of the estimates for the transmitter and monometer are both ST,M = 0.010 inch-H2O = SM,T

• The manufacturer stated accuracy (0.06 inch-H2O) for the transmitter is 6 times larger than SM,T, corresponding to a nearly 100% confidence level

Calibration CorrelationhT,F = 0.985hM - 0.0069

0

0.5

1

1.5

2

2.5

3

0 0.5 1 1.5 2 2.5 3

Tran

smitt

er R

eadi

ng, h

T[in

H20

]

Manometer Pressure Head, hM [in H2O]

hT = hMPerfect Insturment

Response

Fig. 2 Error

• Error in manometer reading increases with pressure• Maximum error magnitude (0.062 inch H2O) is roughly equal to

the manufacturer specified accuracy (0.06 inch H2O)

-0.07

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0 0.5 1 1.5 2 2.5 3

E =

h T-h

M, [

inch

H20

]

Monometer Pressure Head, hM [inch H2O]

Fig. 3 Calibration Deviation

• ST,M characterizes the deviations over the full range of hM

• The ascending deviations are generally positive while the descending ones are negative, which may be caused by hysteresis.

• There are no systematic deviations form the fit correlation, indicating the instrument response is linear.

-0.020

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

0.020

0 0.5 1 1.5 2 2.5 3

e =

h TF

-hT

[inch

H2O

]

hM [inch H2O]

Ascending DataDecending Data

e = -ST,M

e = ST,M

Interpretation of Measurement Question

Transmitter Reading hT,R = 1.9 inch H2O

Expression for Best Estimate h = 1.015hT,R + 0.007 inch H2O

Standard Error of the Estimate for the Measured Pressure

0.010 inch H2O

68% Confidence Interval 1.94 ± 0.01 inch H20

Error in the Reading (if the transmitter had not been

calibratedhT,R - h = -0.04 inch H2O