These calibrated single-axis coil sensors are cost-effective tools for measuring magnetic fields from 5 Hz to 1 MHz. They respond to AC or RF magnetic fields parallel to the coil axis, and produce an analog output voltage calibrated to the magnetic field strength. You display the output voltage on your own instrument (AC or RF voltmeter, multimeter, oscilloscope, or spectrum analyzer with high input impedance).
NIST traceable calibration data is printed and shipped with each sensor. No battery or power supply is needed for these sensors. These are easy, accurate, affordable sensors for magnetic field measurement, EMC / EMI / RFI testing and troubleshooting. The frequency of the sensor output voltage is the same as the frequency of the magnetic field. The frequency range listed in the table below has output voltage at least 0.7 mV per mG from the sensor. The sensors can be used at other frequencies but the output voltage will be lower, as seen in graph below. These sensors do not measure static or DC magnetic fields from magnets, magnetized metal, nor the earth's magnetic field.
|Sensor Model||Frequency Range||Frequency Peak & Freq Response||ITU Bands||Price USD||Availability||Size, Shape*|
|MC910||5 Hz - 400 Hz||60 Hz high peak covers 20-200 Hz||ELF/SLF||$ 190.||In Stock||C4|
|MC858||10 Hz - 300 Hz||58 Hz peak covers 30-100 Hz||ELF/SLF||$ 95.||In Stock||B2 or C3|
|MC876||10 Hz - 400 Hz||76 Hz peak covers 30-200 Hz||ELF/SLF||$ 95.||In Stock||B2 or C3|
|MC95A||20 Hz - 5 kHz||50-1000 Hz flat wideband 1mG=1mV||SLF/ULF||$ 150.||In Stock||B2 or C3|
|MC95R||20 Hz - 50 kHz||1.4 kHz (approx) high sharp peak||SLF/ULF/VLF||$ 125.||In Stock||B2 or C3|
|MC95RW**||20 Hz - 50 kHz||1.6 kHz (approx) high sharp peak||SLF/ULF/VLF||$ 75.||In Stock||B2 or C3|
|MC95-220||20 Hz - 50 kHz||1.8 kHz rounded peak: wideband||SLF/ULF/VLF||$ 125.||In Stock||B2 or C3|
|MC90R||15 Hz - 20 kHz||1.8 kHz (approx) high sharp peak||SLF/ULF/VLF||$ 240.||In Stock||C4|
|MC90-110||15 Hz - 20 kHz||1.8 kHz rounded peak: wideband||SLF/ULF/VLF||$ 240.||In Stock||C4|
|MC90-022||15 Hz - 20 kHz||0.2-20 kHz flat wideband 1mG=5mV||ULF/VLF||$ 190.||In Stock||C4|
|MC110R||5 kHz - 1 MHz||120 kHz (approx) high sharp peak||LF||$ 125.||In Stock||B1|
|MC110A||5 kHz - 1 MHz||120 kHz rounded peak: wideband||LF||$ 125.||In Stock||B1|
|MC190-205||1 kHz - 100 kHz||8 kHz (approx) high peak||VLF||$ 175.||In Stock||C5|
|MC162||2 kHz - 700 kHz||5-700 kHz flat wideband 1mG=1mV||VLF/LF||$ 190.||In Stock||C5|
|MC165||2 kHz - 1 MHz||5-1000 kHz flat wideband 1mG=1mV||VLF/LF||$ 240.||In Stock||C5|
* Sensors are 1" to 5" long, BNC connector: Click Here for Size, Shape, & Connector Table
** MC95RW has 3-wire output, not coax or BNC. Photos at bottom of page.
Graph shows typical sensor output voltage (Volts per Gauss, or mV per mG) at each frequency resulting from a CW magnetic field. Use this graph (or printed cal data), and the sensor output voltage, to determine the Field in Gauss. Individual sensors may vary at their higher frequencies, so calibration data is printed and shipped with each sensor.
To Use the Sensor: Connect the sensor to your display instrument (multimeter, AC or RF voltmeter, spectrum analyzer, or oscilloscope, etc). Place the sensor at the location you want to measure magnetic field strength.
The sensor is single axis and responds to the magnetic field parallel to the sensor axis, which is along the longest dimension of the sensor (parallel to the writing on the sensor label). To see the maximum field, turn the sensor in different directions to find the largest reading, then the sensor axis is parallel to the magnetic field polarization direction. The polarization direction of the field (max reading) is often at right angles to the direction towards the source of the field.
The reading will also increase as you get closer to the source of the field, although multipath reflections can cause variations. Sometimes you won't see exactly the same reading when you check the same location again, this is usually because the sensor is not exactly at the same location and pointing direction. Hold the sensor still. For extremely low frequency (ELF) sensors, jerking or shaking it causes false readings caused by the sensor motion through the earth’s static magnetic field.
To determine the magnetic field: see the measured voltage output from your sensor, and the calibration data table delivered with each sensor (or the graph above) to determine the field at your frequency.
If your instrument can display frequency, you can read the predominant frequency of the magnetic field. You can also use the sensor with a data logger that accepts volts at your frequency.
The length of coax you use can significantly affect readings above 50 kHz, due to coax capacitance. For more information on input impedance and cable length see impedance link below. Sharp bending or yanking of your coaxial cable might break the wires inside the coax, which is usually seen as erratic readings.
Minimum Measurable Field and Resolution: These are determined by the resolution and noise level of your display instrument, the sensor contributes negligible noise.
Maximum Measurable Field: Sensor may be damaged by magnetic fields producing more than 50 Volts output from the sensor. If unsure, better to gradually ramp-up and down the field. Since these are B-dot sensors, suddenly turning the field on or off, or a fast rise or fall time, or other sharp discontinuities in the field like some frequency changes, may cause a transient voltage spike at the output of these B-dot sensors which could damage the sensor (especially the thick cylindrical resonant sensors MC90R and MC90-110). Saturation of the core can cause inaccuracies above 50 Gauss (5 mT) ambient field in air. Sensor sizes C4 and C5 may start to saturate at 25 Gauss (2.5 mT) because those sensor cores are longer: about 4” long.
Temperature Range: Sensors can operate from -30 C to + 55 C (-20 F to +130 F), or in some cases a wider temp range.
Calibration: Calibration standards and instruments are NIST traceable. Each sensor is individually calibrated using a CW (sinusoidal) magnetic field at a number of frequencies, and the calibration data is printed and shipped with each sensor. Since these are passive sensors the calibration is usually accurate for many years.
Display Instrument Impedance: To obtain the calibrated result we recommend a high input impedance, and short coax length. For more information see: Impedance
Technical Notes: These search coils are also known as inductive or B-dot sensors: the voltage output is the time-derivative of the magnetic field. On an oscilloscope if the magnetic field is CW (sinusoidal) then you will see a cosinusoidal output voltage on the scope. On a spectrum analyzer you can typically see the Fourier frequency components of the magnetic field if they are within the frequency passband of the sensor. When exposed to a sharp rise or drop in magnetic field (like an impulse or spike or rectangular “box-car” field pulse), the voltage output from the sensor will show a spike due to the sudden change in field, and also the sensor output may continue to “ring” for a few milliseconds at natural resonant frequencies of the sensor circuit and higher frequency parasitics. These sensors can also be used for vibration monitoring to measure mechanical vibrations, by using the earth's magnetic field.
If a sensor is broken it is usually due to an intermittent coaxial connector, or broken coax center conductor due to sharp bending, or damaged sensor due to a fast change in the magnetic field which produced a voltage spike in the sensor coil.
In elliptically polarized fields the maximum reading of the sensor will be parallel to the major axis of the polarization ellipse, so these single-axis sensors avoid some errors seen for most triple-axis AC gaussmeters in elliptically or circularly polarized fields and near 3-phase power lines due to sequential sampling of X,Y,Z field polarizations by most triple-axis meters.