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SENSOR
Appendix B Test Overview
SMT-200 Operations and Technical Manual 2.00/R1
101
B.11 Geophone String Resistance Calculation
Strings generally fall into two groups, series and series parallel.
B.11.1 Series String
1. First find the total resistance (Rt) of one geophone
Rt
Rc Rd
Rc Rd
=
×
+
Example..
Rt =
×
+
=
375 1000
375 1000
273Ω
Rd = Damping Resistor
Rc = Coil Resistance
2. Next multiply the above figure by the number of geophones in the string
Rs n Rt=×
Example..
Rs =× =6 273 1638 Ω
Rs = String Resistance Rt = 273Ω
N = Number of geophones n = 6
3. String resistance in this case is 1638 Ω.
B.11.2 Series Parallel String
First find the resistance of one parallel branch. For example if the string was configured as a 6 x 3
string this would mean there are 6 series geophones and 3 parallel branches. The formulas used in
B.8.1 can be used for this. In that particular instance we would end up with a branch resistance of
1638 Ω. Divide this number by the number of branches.
Rt
Rb
n
=
546
3
1638
==Rt Ω
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