This page applies to the sensors shown at Sensors 5 Hz-1 MHz . Each sensor is individually calibrated to a CW (sinusoidal) magnetic field at each frequency. Calibration standards and instruments are NIST traceable.
Individual sensors may show considerable variation at frequencies above 300 kHz and near resonance peaks, for those sensor models the calibration data is also recorded and shipped with the sensor, as shown in "Calibration" column in table at Sensors 5 Hz-1 MHz.
These sensors were calibrated using RF voltmeters with input impedance equal to 10 Mohm in parallel with capacitance less than 30 pF. At ELF (below 3 kHz) we may use voltmeters with input impedance of 1 Mohm in parallel with approximately 100 pF.
We suggest that you use a high-impedance instrument with low shunt capacitance for displaying the output AC voltage from these sensors, because the instrument input impedance and parallel capacitance can affect your readings, especially above about 50 kHz.
If your test instrument uses a lower input impedance (such as 50 ohms or 1 Mohm) then we recommend that you use a high impedance adapter or high impedance probe with low capacitance for your display instrument, so that you can obtain the calibrated sensor results.
At frequencies above 50 kHz, the length of the coaxial cable used for your measurements can significantly affect the results. If the sensor has no built-in coax cable (shown in the table at Sensors 5 HZ - 1 MHz), then for calibration we connected a 3-foot long coaxial cable to connect the sensor to the voltmeter, which adds approximately 30 pF per foot, in shunt to the meter.
Since these are passive sensors the calibration is usually accurate for many years. If the sensor seems to be broken it is usually due to an intermittent coaxial connector, or broken coax cable center conductor, or a damaged sensor due to a very large or fast changing magnetic field which produced more than 50 Volts at the sensor output.
A narrow-bandwidth resonant frequency (fo) is seen for some sensors (MC95R, MC95RW, MC90R, MC110R) where a high output peak is seen. The output impedance you present to the sensor can affect the frequency of fo and the output level near fo and higher frequencies.