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 Data||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||$ 195.||In Stock||Tested & Printed||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 & Printed||3-wire connector||Rectangular||2.1 x1.6 x1.2”||52x40x29mm|
|MC910||15 Hz - 300 Hz||$ 195.||In Stock||Tested & Printed||BNC(m) on coax||Thick cylinder||4.0 x 1.125”||102x29mm|
|MC90R||15 Hz - 50 kHz||$ 195.||In Stock||Tested & Printed||BNC(m) on coax||Thick cylinder||4.0 x 1.125”||102x29mm|
|MC110A||5 kHz - 1 MHz||$ 95.||In Stock||Tested & Printed||BNC(f)||Small square||1x1x0.8”||25x25x20mm|
|MC110R||5 kHz - 1 MHz||$ 95.||In Stock||Tested & Printed||BNC(f)||Small square||1x1x0.8”||25x25x20mm|
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 higher frequencies, so printed calibration data is shipped with most sensor models.
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 printed 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 a number of frequencies. For some models the calibration data is also printed 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 here: Calibrations.
Technical Notes: Coils 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 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 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 & higher frequency parasitics.
These sensors can also be used for vibration monitoring to measure mechanical vibrations, using the earth's magnetic field.
In elliptically polarized fields the maximum reading of the sensor will be 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.