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Magnetic Sensors for 5 Hz-1 MHz

These calibrated single-axis coil sensors are accurate 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 which is accurately calibrated to the magnetic field strength. You display the sensor output voltage on your own instrument (AC or RF voltmeter, multimeter, oscilloscope, or spectrum analyzer with high input impedance). 

No battery or power supply is needed for the sensors. These are easy, accurate, affordable sensors for magnetic field measurement, test and EMC / EMI / RFI troubleshooting. The frequency of the sensor output voltage is the same as the frequency of the magnetic field. These sensors do not measure static or DC magnetic fields from magnets, magnetized metal, nor the earth's 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 the graph.  

Sensor Model Frequency Range Price USD Availability Calibration Connector Case Style Size, inches Size, mm
MC95 25 Hz - 3 KHz  $ 150  In Stock Tested BNC(f) Rectangular 2.1" x1.6 x1.2" 52x40x29mm
MC162 2 kHz - 1 MHz  $ 150.  In Stock Tested & Recorded BNC(m) on coax Thin cylinder 5.25 x 0.75” 133x19mm
MC858 15 Hz - 180 Hz  $ 70.  In Stock  Tested BNC(f) Rectangular 2.1 x1.6 x1.2” 52x40x29mm
MC876 20 Hz - 300 Hz  $ 70.  In Stock  Tested BNC(f) Rectangular 2.1 x1.6 x1.2” 52x40x29mm
MC95RW 20 Hz - 50 kHz  $ 95.  In Stock Tested & Recorded 3-wire connector Rectangular 2.1 x1.6 x1.2” 52x40x29mm
MC910 15 Hz - 300 Hz  $ 195.  In Stock Tested & Recorded BNC(m) on coax Thick cylinder 4.0 x 1.125” 102x29mm
MC90R 15 Hz - 50 kHz  $ 195.  In Stock Tested & Recorded BNC(m) on coax Thick cylinder 4.0 x 1.125” 102x29mm
MC110A 5 kHz - 1 MHz  $ 95.  In Stock Tested & Recorded BNC(f) Small square 1x1x0.8” 25x25x20mm
MC110R 5 kHz - 1 MHz  $ 95.  In Stock Tested & Recorded BNC(f) Small square 1x1x0.8” 25x25x20mm


Graph shows sensor output voltage caused by a CW magnetic field (Volts per Gauss, or mV per mG) at each frequency. Use this graph or recorded cal data, and the sensor output voltage, to determine the Field in Gauss. 

  • Examples: at your frequency if the Volts per Gauss = 1 (on vertical axis), and you are measuring 80 mV, then the field = 80 mG. 
  • Or, at your frequency:           if the Volts per Gauss = 8 (on vertical axis), and you are measuring 80 mv, then the field = 10 mG. 
  • If your display instrument is measuring RMS volts then you are measuring RMS magnetic field strength.
  • If your display instrument is measuring Peak volts then you are measuring Peak magnetic field strength. 

To Use the Sensor: Connect the sensor to your display instrument (multimeter, AC or RF voltmeter, spectrum analyzer, or oscilloscope, etc). For best accuracy the input impedance of your display instrument should be at least 1 Megaohm for measurements below 100 kHz, or at least 10 Megaohms from 100 kHz to 1 MHz.

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.

Use the measured voltage and the graph above (or calibration data if recorded for your sensor) to determine the magnetic field. 

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 calibration info 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: Is determined by the noise level of your display instrument, the sensor contributes negligible noise.

Maximum Measurable Field: Sensor may be damaged by strong magnetic fields producing more than 50 Volts output. If unsure, better to gradually ramp-up and down the field. Suddenly turning a strong field on or off causes a voltage spike at output of sensor which could exceed 50 Volts. Saturation of the core can cause inaccuracies above 50 Gauss ambient field in air.
Models MC162, MC910, and MC90R may start to saturate at 25 Gauss or higher, because those sensor cores are 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: Each sensor is calibrated using a CW (sinusoidal) magnetic field at each frequency. For some models the calibration data is also recorded and shipped with the sensor (if stated in the table above). Calibration standards and instruments are NIST traceable. For more information on how these sensors are calibrated, click calibration

Technical NotesCoils are known as “B-dot” sensors since the voltage output is the time-derivative of the magnetic field. On an oscilloscope, if the magnetic field you are measuring is CW (sinusoidal) then you will see a sinusoidal output voltage waveform on the scope. On a spectrum analyzer you can typically see the Fourier frequency components of the magnetic field if 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” 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 some natural resonant frequencies of the sensor circuit and due to higher frequency parasitics. In elliptically polarized fields the maximum reading of the sensor will be the major axis of the polarization ellipse, so these single-axis sensors therefore avoid some errors seen by most triple-axis AC gaussmeters in elliptically or circularly polarized fields and near 3-phase power lines. These sensors can also used in vibration monitoring systems to measure mechanical vibrations using the earth's magnetic field.