Campbell Scientific CS11-L Current Transformer - Manual (Page 31)

Appendix A. Theory of Operation
The formula for a transformer is as follows (Equation A):
i
1
• n
1
= i
2
• n
2
Equation A
Where i = amps and n = number of turns or windings
And where n
1
is the primary winding and n
2
is the secondary
With the current transformer, the primary coils or windings are minimized to
avoid removing power out of the circuit, but still have a signal large enough to
measure (see FIGURE A-6).
Only 1 pass Many windings
FIGURE A-6. Windings schematic
A small amount of current is transferred to the secondary coil.
Find the current induced on the secondary windings by solving for i
2
:
i
2
= i
1
• n
1
/n
2
Equation B
For example: The CS11-L current transducer has an n
2
value of 2000
windings. If 20 amps pass through the primary winding, the following
amperage is produced on the secondary winding:
i
2
= 20 • (1/2000) = 0.01 amp on secondary winding
A.3 Converting a Milliamp Signal to a Millivolt Signal
After the current is transformed from one level to another level, the amperage
signal must be converted to a voltage signal so that the datalogger can measure
it.
Use Ohm’s Law (Equation C) to convert amperage to voltage:
E = I • R (E=Volts, I = Amps, R = Ohms) Equation C
For example: Using the previous example:
E = 0.01 amps • R
A-3