LGT 4.5Hz Sensor Testing by Micheal Cranford

Web Page Created by L. Cochrane Oct. 22, 2013


 

LGT-4.5 Geophone Measurements

R1

R2

M (gm)

Loaded

No Load

D=0.707

D=1.000

100000

16667

11.3

Damping

Damping

Damping

Damping

Factor

Factor

Resistance

Resistance

A1

A2

K

V0-

T1

G

X Axis (East/West)

0.657

0.1072

0.0070

1251

    R1 Positive Step

0.650

0.638

17897

3119

0.1031

0.0070

1268

0.0339

0.0390

0.282

    R2 Positive Step

0.712

0.0944

0.0039

    R1 Negative Step

0.663

0.650

21386

3152

0.1112

0.0069

1235

0.0352

0.0394

0.291

    R2 Negative Step

0.723

0.1016

0.0038

Y Axis (North/South)

0.685

0.1123

0.0059

1437

    R1 Positive Step

0.680

0.666

33777

3861

0.1066

0.0058

1419

0.0340

0.0402

0.278

    R2 Positive Step

0.749

0.0974

0.0028

    R1 Negative Step

0.690

0.676

45804

4101

0.1180

0.0059

1454

0.0352

0.0418

0.293

    R2 Negative Step

0.761

0.1075

0.0027

Z Axis (Up/Down)

0.590

0.1234

0.0124

1449

    R1 Positive Step

0.608

0.593

12762

3306

0.1362

0.0123

1502

0.0341

0.0584

0.309

    R2 Positive Step

0.681

0.1225

0.0066

    R1 Negative Step

0.570

0.556

8853

2759

0.1105

0.0125

1395

0.0354

0.0449

0.243

    R2 Negative Step

0.638

0.1012

0.0075

No Load

No Load

D=0.707

D=0.707

D=1.000

D=1.000

100K Ohm

Generating

Damping

Transducer

Damping

Transducer

Damping

Transducer

Resonant

Coil DC

Factor

Gain

Resistance

Gain

Resistance

Gain

Frequency

Resistance

Measurement Units

V / (cm/S)

Ohms

V / (cm/S)

Ohms

V / (cm/S)

Hertz

Ohms

X Axis (East/West)

0.644

0.287

19517

0.282

3137

0.256

4.627

381

Y Axis (North/South)

0.671

0.287

39186

0.284

3982

0.262

4.322

382

Z Axis (Up/Down)

0.576

0.277

10653

0.268

3032

0.246

3.786

383

 

Note:

The two large blocks at the bottom show the final output, including the damping factors, the damping resisters and the transduction gains for the three different damping factors.

Addition Information:

        R1 is a 100K 1% resistor in series with the signal generator, while R2 represents the thevenin equivalent generator
        source resistance after switching in a 20K 1% resistor in parallel with the geophone.  Hence each geophone is tested
        with 100K and 16.667K damping resistors to determine the various parameters. The resonant frequencies were only
        measured with the 100K damping resistor. Both positive and negative step responses were measured and an average
        computed for the final results. Every cell with a pale yellow-green background shows the data entered and all of the
        remaining plain background cells show the calculated results.  Also note that the moving mass is in units of grams.

Summary:

        Based on the very small sample size for the horizontal geophones (2), I'm seeing a -4% to +3% variation in the resonant
        frequency and about a +/-0% variation in the open circuit damping factor, all of which are well within the +/-10% specs.
        The vertical geophone has a -19% resonant frequency deviation (obviously a much lower frequency than the spec range)
        and a -4% damping factor deviation, both are relative to the manufacturers nominal values. All three geophones are well
        within their +/-5% coil resistance specifications.


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