Geokon 3900 Manuel utilisateur

Instruction Manual

Model 3900

Embedment Strain Gauge

No part of this instruction manual may be reproduced, by any means, without the written consent of Geokon®.

The information contained herein is believed to be accurate and reliable. However, Geokon®assumes no responsibility for errors,

omissions or misinterpretation. The information herein is subject to change without notification.

(Doc REV E, 04/30/19)

Warranty Statement

Geokon warrants its products to be free of defects in materials and workmanship, under normal

use and service for a period of 13 months from date of purchase. If the unit should malfunction,

it must be returned to the factory for evaluation, freight prepaid. Upon examination by Geokon,

if the unit is found to be defective, it will be repaired or replaced at no charge. However, the

WARRANTY is VOID if the unit shows evidence of having been tampered with or shows

evidence of being damaged as a result of excessive corrosion or current, heat, moisture or

vibration, improper specification, misapplication, misuse or other operating conditions outside of

Geokon's control. Components which wear or which are damaged by misuse are not warranted.

This includes fuses and batteries.

Geokon manufactures scientific instruments whose misuse is potentially dangerous. The

instruments are intended to be installed and used only by qualified personnel. There are no

warranties except as stated herein. There are no other warranties, expressed or implied, including

but not limited to the implied warranties of merchantability and of fitness for a particular

purpose. Geokon is not responsible for any damages or losses caused to other equipment,

whether direct, indirect, incidental, special or consequential which the purchaser may experience

as a result of the installation or use of the product. The buyer's sole remedy for any breach of this

agreement by Geokon or any breach of any warranty by Geokon shall not exceed the purchase

price paid by the purchaser to Geokon for the unit or units, or equipment directly affected by

such breach. Under no circumstances will Geokon reimburse the claimant for loss incurred in

removing and/or reinstalling equipment.

Every precaution for accuracy has been taken in the preparation of manuals and/or software,

however, Geokon neither assumes responsibility for any omissions or errors that may appear nor

assumes liability for any damages or losses that result from the use of the products in accordance

with the information contained in the manual or software.

TABLE of CONTENTS

1. INTRODUCTION .................................................................................................................................................. 1

2. INSTALLATION.................................................................................................................................................... 1

3. TAKING READINGS ............................................................................................................................................ 1

3.1 CIRCUIT DIAGRAM .............................................................................................................................................. 2

3.2 USING THE GEOKON GK-502 READOUT BOX ..................................................................................................... 2

4. DATA REDUCTION.............................................................................................................................................. 3

4.1 DISPLACEMENT CALCULATION ........................................................................................................................... 3

4.2 STRAIN CALCULATION........................................................................................................................................ 3

4.3 TEMPERATURE CORRECTION FACTOR................................................................................................................. 4

APPENDIX A. SPECIFICATIONS .......................................................................................................................... 5

APPENDIX B. THERMISTOR TEMPERATURE DERIVATION ...................................................................... 6

APPENDIX C. TYPICAL CALIBRATION REPORT ........................................................................................... 7

FIGURES

FIGURE 1-CIRCUIT DIAGRAM ....................................................................................................................................... 2

FIGURE 2-TYPICAL CALIBRATION REPORT .................................................................................................................. 7

TABLES

TABLE 1-INPUT CONNECTIONS .................................................................................................................................... 1

TABLE 2-SPECIFICATIONS ............................................................................................................................................ 5

TABLE 3-THERMISTOR RESISTANCE VERSUS TEMPERATURE ...................................................................................... 6

EQUATIONS

EQUATION 1-DISPLACEMENT....................................................................................................................................... 3

EQUATION 2-STAIN CALCULATION WITH TEMPERATURE CORRECTION....................................................................... 4

EQUATION 3-RESISTANCE TO TEMPERATURE .............................................................................................................. 6

1. INTRODUCTION

The Model 3900 Embedment Strain Gauge is designed for the measurement of dynamic strains

in concrete structures and soils. It comprises a full-bridge strain gauge proving ring element

coupled in series with a tension spring which is stretched between two end flanges. An outer

PVC tube sealed with O-rings provides a waterproof housing. The end flanges are embedded and

move in accordance with the surrounding material. The voltage signals from the strain gauge are

transmitted via cable to the readout location.

The strain gauge can be read out by means of the Geokon Model 502 Readout Box or by a

applying a 2 to 12 Volt excitation to the input leads and reading the corresponding millivolt

output. The output at full range is approximately 3 mV/V. The standard wiring for use with the

GK-502 readout box is configured to compensate for the use of long cables by the remote

sensing of the input voltage at the sensor. A Thermistor is included inside the sensor to measure

temperatures. This requires a cable with four shielded pairs of conductors.

2. INSTALLATION

The embedment gauge is delivered with the sensor set at an approximately midrange position

ready for installment. The standard range is ± 2500 microstrains. (Other ranges are available).

An initial test can be conducted by connecting the strain gauge to the GK-502 Readout Box or to

a regulated voltage supply. Movement of the end flanges should produce a corresponding change

in the gauge output. At no time should the end flanges be twisted or pulled beyond the range of

the sensor as this could permanently damage the gauge.

The gauge should be installed directly in the concrete or soil by hand. Large aggregate should be

removed from the area immediately surrounding the sensor. The use of vibrators immediately

next to the gauge should be avoided. The standard cable has a thick PVC jacket and can be

placed directly in the concrete.

3. TAKING READINGS

Connect the ten-pin connector to the GK-502 readout box or connect the bare wires to a voltage

supply and millivoltmeter as follows:

Bendix Pin

Circuit Label

Description

Geokon Purple Cable

S-

Bridge Output -

White's Black

P+

Bridge Excitation +

Red

P-

Bridge Excitation -

Red's Black

S+

Bridge Output +

White

No Connection

Ground for shield

Shield

Thermistor

Blue

Thermistor

Blue’s Black

RS+

Remote Sense +

Green

RS-

Remote Sense -

Green's Black

Table 1 - Input Connections

3.1 Circuit Diagram

P-

P+

S+

S-

RS+

RS-

Strain Gage

Figure 1 - Circuit Diagram

3.2 Using the Geokon GK-502 Readout Box

The user is referred to the GK-502 Instruction Manual for additional information on the

following instructions:

1) Connect the embedment gauge to the readout box by means of the 10-pin input connector.

2) Press the ‘ON/OFF’ button power switch to the "ON" position.

3) Press the ‘UNITS’ button until the UNITS displayed are mV/V.

4) Read the display and record.

5) See the GK-502 Instruction Manual for further instructions.

4. DATA REDUCTION

4.1 Displacement Calculation

The basic units utilized by Geokon for measurement and reduction of data from Model 3900

Embedment Strain Gauges are mV/V

If a GK-502 readout box is in use mV/V can be displayed directly.

The displacement Dis given by the equation:

D = ((R1- R0) ×C

Equation 1 - Displacement

Where;

D is the displacement in the units given on the calibration report provided with the instrument.

R0is the initial GK-502 reading in mV/V.

R1is the current GK-502 reading in mV/V.

C is the calibration factor in millimeters/mV/V, or inches/mV/V as supplied on the Cal Sheet.

(See Appendix C. for a sample calibration report.)

If a regulated power supply and a millivoltmeter are used, then calculate the mV/V by dividing

the displayed millivolt output by the voltage input measured at the sensor using the remote signal

leads, (Green and Green’ Black).

4.2 Strain Calculation

To calculate the strain ε,divide the measured displacement Dby the gauge length L.

The standard length for Lis 203 mm (Eight inches)

Example: Using a GK-502, R0= -0.8640 and R1= -0.5563, C = 0.05193 inches/mV/V.

Strain ε = ((-0.5563-(-0.8640) x 0.05193/8 = +2000 microstrain (tension)

Note that an increasing reading denotes a tensile strain.

4.3 Temperature Correction Factor

Tests have shown that the temperature effect is such that the embedment gauge reading goes

down (compression) as the temperature goes up and the required temperature correction factor is

plus six microstrains per °C.

So, for example, using the GK-502 (displaying mV/V) to take the readings, and a standard eight-

inch-long gauge, where Cis given in inches/mV/V, the calculation for strain S, corrected for

temperature change (T1- T0)measured in degrees Centigrade, is:

S = (R1- R0) ×C/8 + 6(T1- T0) microstrain

Equation 2 - Stain Calculation with Temperature Correction

Where Cis given in mm/mv/v the equivalent equation is

S = ((R1- R0) ×C/203 + 6(T1- T0) microstrain

APPENDIX A. SPECIFICATIONS

Standard Range¹: 5000 microstrain

Accuracy: ± 0.1% FS

Linearity: <0.5% FSR

Resolution: ± 0.025% FSR

Repeatability: 0.1% FSR

Temperature Effect: 0.12% FSR/°C

Temperature Range:

−20 to +80° C

0 to 110° F

Active Gauge Length2203 mm

Input Resistance: 350Ω

Output Resistance: 350 Ω

Excitation Voltage: 2 to 15 V DC

Maximum Excitation Voltage: 30 V

Cable Type:

Four twisted pair (eight conductor) 22 AWG

Foil shield, PVC jacket, nominal OD=9.5 mm (0.375")

Table 2 - Specifications

Notes

¹ Other ranges are available on request.

2 Other gauge lengths available on request.

APPENDIX B. THERMISTOR TEMPERATURE DERIVATION

Thermistor Type: YSI 44005, Dale #1C3001-B3, Alpha #13A3001-B3

Resistance to Temperature Equation:

T= 1

A+B(LnR)+C(LnR)3-273.15 °C

Equation 3 - Resistance to Temperature

Where;

T =Temperature in °C.

LnR =Natural Log of Thermistor Resistance

A =1.4051 ×10-3

B =2.369 ×10-4

C =1.019 ×10-7

Note: Coefficients calculated over the −50 to +150°C. span.

Ohms

Temp

Ohms

Temp

Ohms

Temp

Ohms

Temp

Ohms

Temp

201.1K

-50

16.60K

-10

2417

+30

525.4

+70

153.2

+110

187.3K

-49

15.72K

-9

2317

507.8

149.0

111

174.5K

-48

14.90K

-8

2221

490.9

145.0

112

162.7K

-47

14.12K

-7

2130

474.7

141.1

113

151.7K

-46

13.39K

-6

2042

459.0

137.2

114

141.6K

-45

12.70K

-5

1959

444.0

133.6

115

132.2K

-44

12.05K

-4

1880

429.5

130.0

116

123.5K

-43

11.44K

-3

1805

415.6

126.5

117

115.4K

-42

10.86K

-2

1733

402.2

123.2

118

107.9K

-41

10.31K

-1

1664

389.3

119.9

119

101.0K

-40

9796

1598

376.9

116.8

120

94.48K

-39

9310

1535

364.9

113.8

121

88.46K

-38

8851

1475

353.4

110.8

122

82.87K

-37

8417

1418

342.2

107.9

123

77.66K

-36

8006

1363

331.5

105.2

124

72.81K

-35

7618

1310

321.2

102.5

125

68.30K

-34

7252

1260

311.3

99.9

126

64.09K

-33

6905

1212

301.7

97.3

127

60.17K

-32

6576

1167

292.4

94.9

128

56.51K

-31

6265

1123

283.5

92.5

129

53.10K

-30

5971

1081

274.9

90.2

130

49.91K

-29

5692

1040

266.6

87.9

131

46.94K

-28

5427

1002

258.6

85.7

132

44.16K

-27

5177

965.0

250.9

83.6

133

41.56K

-26

4939

929.6

243.4

81.6

134

39.13K

-25

4714

895.8

236.2

79.6

135

36.86K

-24

4500

863.3

229.3

77.6

136

34.73K

-23

4297

832.2

222.6

75.8

137

32.74K

-22

4105

802.3

216.1

73.9

138

30.87K

-21

3922

773.7

209.8

72.2

139

29.13K

-20

3748

746.3

203.8

100

70.4

140

27.49K

-19

3583

719.9

197.9

101

68.8

141

25.95K

-18

3426

694.7

192.2

102

67.1

142

24.51K

-17

3277

670.4

186.8

103

65.5

143

23.16K

-16

3135

647.1

181.5

104

64.0

144

21.89K

-15

3000

624.7

176.4

105

62.5

145

20.70K

-14

2872

603.3

171.4

106

61.1

146

19.58K

-13

2750

582.6

166.7

107

59.6

147

18.52K

-12

2633

562.8

162.0

108

58.3

148

17.53K

-11

2523

543.7

157.6

109

56.8

149

Table 3 - Thermistor Resistance Versus Temperature

55.6

150

Table des matières

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