Calibration of these sensors is done using National Institute of Standards and Technology (NIST) traceable test instruments and procedures. All sensors are individually tested to ensure accuracy. For many sensor models we also record the calibration test data and ship it with the sensor (see sensor table).
We calibrate each sensor using voltmeters with input impedance equal to 10 Mohm in parallel with <30 pF. At ELF we may use voltmeters with input impedance of 1 Mohm in parallel with approximately 100 pF.
We suggest that you also use a high-impedance instrument for displaying the output AC voltage from the sensor, because the instrument input impedance and parallel capacitance can affect your readings, especially at the higher frequencies.
If your test instrument uses a much lower input impedance (such as 50 ohms used in some oscilloscopes and most spectrum analyzers) then you should use a high impedance adapter with your instrument to obtain calibrated sensor results.
If the sensor has no built-in cable (that is all our sensors except Case Style B), then for our calibration we also used a 4-foot long coaxial cable to connect the sensor to the voltmeter, which adds approximately 30 pF per foot, in shunt to the meter (MC110A and MC110R used a 3-foot long coax). The length of your cable can significantly affect your results at higher frequencies.
Since these are passive sensors the calibration is usually accurate for many years. If the sensor seems to be broken after some use it is usually due to an intermittent coax connector, or broken coax center conductor, or exposure to an excessively large magnetic field spike which produced 50 Volts or more at the sensor output.
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