Magnetic Sensors for 5 Hz-1 MHz

These calibrated magnetic field sensors or probes are accurate cost-effective tools for measuring CW sine wave magnetic fields from 5 Hz to 1 MHz. These single-axis "B-dot" coil sensors respond to magnetic fields parallel to the coil axis; they produce an output voltage calibrated to the AC or RF 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). The frequency of the sensor output voltage is the same as the frequency of the magnetic field.

NIST traceable calibration certificate with data is printed and shipped with each sensor. No battery or power supply is needed for the sensors. These are easy-to-use affordable sensors for magnetic field measurement, EMC / EMI / RFI testing, and troubleshooting. These sensors do not measure static or DC magnetic fields, for example from motionless magnets or the earth's magnetic field, unless the sensor is vibrating or rotating.

Sensor Model	Frequency Range	Frequency Response Description	ITU Bands	Price USD	Availability	Size, Shape*
MC910	5 Hz - 600 Hz	60 Hz High peak 20-200 Hz	ELF/SLF	$ 200.	In Stock	C4
MC858	10 Hz - 400 Hz	58 Hz Resonant peak 30-100 Hz	ELF/SLF	$ 95.	In Stock	B2 or C3
MC876	10 Hz - 600 Hz	76 Hz Resonant peak 30-200 Hz	ELF/SLF	$ 95.	In Stock	B2 or C3

MC06	50 Hz - 120 Hz	61 Hz Resonant peak, small size	SLF	$75	In Stock	B1wm
MC14	40 Hz - 400 Hz	135 Hz Resonant peak, small size	SLF	$125	Special order	B1wm
MC19	40 Hz - 1 kHz	190 Hz Resonant peak, small size	SLF/ULF	$75	In Stock	B1wm

MC95A	10 Hz - 10 kHz	30-3000 Hz Flat wideband 1mG=1mV	SLF/ULF/VLF	$ 175.	In Stock	B2 or C3
MC95R	10 Hz - 50 kHz	1.6 kHz (approx) High resonant peak	SLF/ULF/VLF	$ 125.	In Stock	B2 or C3
MC95Rw	10 Hz - 50 kHz	1.6 kHz (approx) High resonant peak	SLF/ULF/VLF	$ 95.	In Stock	B2 or C3
MC95-220	10 Hz - 30 kHz	1.6 kHz Rounded peak: wideband	SLF/ULF/VLF	$ 150.	In Stock	B2 or C3

MC90R	10 Hz - 20 kHz	1.8 kHz (approx) High resonant peak	SLF/ULF/VLF	$ 250.	In Stock	C4
MC90-110	10 Hz - 20 kHz	1.8 kHz Rounded peak: wideband	SLF/ULF/VLF	$ 200.	In Stock	C4
MC90-022	10 Hz - 20 kHz	0.2-20 kHz Flat wideband 1mG=5mV	ULF/VLF	$ 200.	In Stock	C4

MC110R	2 kHz - 1 MHz	120 kHz (approx) High resonant peak	VLF/LF	$ 125.	In Stock	B1
MC110A	2 kHz - 1 MHz	120 kHz Rounded peak: wideband	VLF/LF	$ 125.	In Stock	B1

MC190-205	1 kHz - 150 kHz	8 kHz (approx) High peak	VLF	$ 150.	In Stock	C5
MC161	1 kHz - 500 kHz	2-500 kHz Flat wideband 1mG=1mV	VLF/LF	$ 150.	In Stock	C5
MC162	1 kHz - 700 kHz	2-700 kHz Flat wideband 1mG=1mV	VLF/LF	$ 200.	In Stock	C5
MC165	1 kHz - 1 MHz	2-999 kHz Flat wideband 1mG=1mV	VLF/LF	$ 250.	In Stock	C5

* Sensors are 1" to 5" long. Click Here for Size, Shape, & Connectors. Photos at bottom of page.

Graph above shows each sensor model output voltage (as Volts output per Gauss, or mV output per mG field) at each frequency, when placed in a continuous sine wave (CW) magnetic field at that frequency. Use this graph (or printed calibration data), and the sensor output voltage, to determine the magnetic field in Gauss. The graph is accurate for a continuous sine wave (CW) magnetic field. Individual sensors may vary, so calibration data is printed and shipped with each sensor.

Examples: at your frequency if the Volts per Gauss = 1 (on vertical axis), and you are measuring 80 mV, then the CW field = 80 mG. (80mV /1 = 80mG)
Or, at your frequency if the Volts per Gauss = 8 (on vertical axis), and you are measuring 80 mv, then the CW field =10 mG. (80mV /8 = 10mG)
Or, at your frequency if the Volts per Gauss = 5 (on vertical axis), and you are measuring 3 V, then the CW field =0.6 G. (3V /5 = 0.6 G)
If your display instrument is measuring RMS volts then you are measuring RMS magnetic field strength. (RMS is recommended).
If your display instrument is measuring Peak volts then you are measuring Peak magnetic field strength.
Unit conversion: 10G = 1mT, 1 mG = 0.1 uT. 1 kA/m = 1.26 mT = 12.6 G in air.

To Use the Sensor: Connect the sensor to your display instrument (multimeter, AC or RF voltmeter, spectrum analyzer, or oscilloscope, etc). Place the center of 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). The sensing area is along most of the length of sensor axis, so if the field is spatially non-uniform it will be averaged over the length of the sensor.

To find the maximum field polarization, turn the sensor in different directions to see the largest reading, then the sensor axis is parallel to the maximum 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 the immediate surroundings, multiple sources, and the sensor orientation (pointing direction) 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 orientation. Hold the sensor still, because vibrating, shaking, or quick movements can cause extraneous readings due to sensor acceleration through the earth’s static magnetic field.

To measure the magnetic field: Measure the alternating (AC or RF) voltage output from your sensor, then reference the graph above (or the calibration data delivered with each sensor) at your frequency to determine the magnetic field strength.

Minimum Measurable Field and Resolution: These are determined by the resolution and noise level of your display instrument. The sensors are passive devices and contribute negligible thermal noise.

Maximum Measurable Field: Sensors may be damaged by magnetic fields producing more than 50 Volts output from the sensor. Also, saturation of the core can cause inaccuracies above 50 Gauss (5 mT) field. The longest sensors (sizes C4 and C5) may start to saturate at 25 Gauss (2.5 mT). Since these are B-dot sensors, a fast change in the field can cause output voltage to peak which could damage the large sensors MC90R and MC90-110 with high outputs. If unsure then best to gradually ramp-up and down the field strength.

Temperature Range: Sensors can operate from -30 C to + 55 C (-22 F to +131 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 sine wave magnetic field at a number of frequencies, and the calibration data is printed and shipped with each sensor. Calibration is usually accurate for many years for these passive sensors. Calibration results may vary near resonant frequencies and above 500 kHz.

Instrument Impedance and Coax: To display the calibrated output voltage from the sensor we recommend you use an instrument with high input impedance. The length of coaxial cable you use can also significantly affect readings above 30 kHz, due to coax capacitance, see Impedance

Sinusoidal and Non-Sinusoidal Fields: These coils are known as "B-dot" sensors since the voltage output is the time-derivative of the magnetic field. So if the magnetic field is a continuous CW sine wave, then the sensor output voltage is a cosine voltage wave at the same frequency.

For non-sinusoidal waveforms the output voltage is also the first derivative (B-dot) of the magnetic field. So when exposed to a rapid large change in the magnetic field (like switching the field on or off, or square wave or spike in the field), then the sensor output voltage will show a peak or bump, due to the large fast change in the field giving a large first derivative.

Some sensors are described as "resonant" in the Description column of table at top of this page. Their frequency peak is the resonant frequency. Those "resonant" models will "ring" for a few milliseconds if briefly exposed to their natural resonant frequency, for example due to rapid changes in a non-sinusoidal field like a square wave field. So it is recommended to use resonant models only for sinusoidal CW fields to avoid distortion of the output due to ringing.

For screenshots and more measurement info see www.magneticsciences.com/measurement-notes

All these sensors can also be used for vibration monitoring to measure mechanical vibrations or rotations using the sensor's motion through the earth's magnetic field or through the field of a nearby magnet.