CMA ML51m User guide

CMA ML51m User guide
MAGNETIC FIELD SENSOR ML51M
USER’S GUIDE
CENTRE FOR MICROCOMPUTER APPLICATIONS
http://www.cma-science.nl
Short description
The Magnetic Field sensor ML51m measures magnetic field strength in the range of
‐1000 to 3000 Gauss (‐100 .. 300 mT). The sensor uses a Hall‐element as its sensing
element. This element is mounted at the tip of the stainless steel tube.
The face of Hall element is directed perpendicular to the direction of the stainless
steel tube and the sensor is most sensitive when the tube is positioned parallel to
magnetic field lines. The sensor is therefore very suitable for measuring magnetic
field inside coils or near permanent magnets.
The Magnetic Field sensor is an I2C digital sensor, which gives calibrated values of
the measured quantity. This sensor can only be connected to special interfaces that
support I2C digital sensors like the CMA MoLab interface. The sensor cable needed
to connect the sensor to an interface is not supplied with the sensor (sensor cables
are supplied with interfaces).
Note:
The values obtained by the sensor will be sensitive to the position in magnetic field
and the orientation of the sensor to the field direction. A false low value could be
achieved if the direction of magnetic field is not parallel to the direction of the sensor
tube.
Sensor specifications
The Magnetic Field sensor ML51m is a digital sensor that converts the measured
magnetic field strength value to a digital value via 14‐bit analog‐to‐digital
conversion. The resolution of the senor is 0.244 gauss. The maximal sampling
frequency of the sensor is 1000 Hz.
Collecting data
This Magnetic Field sensor works only with specific interfaces. The sensor will be
automatically detected when connected to such an interface.
For detailed information about measurements with sensors consult the User
Manuals of the interface and the Coach 6 software.
Calibration
The Magnetic Field sensor is supplied with a factory calibration in gauss (G). The
Coach 6 program allows shifting the pre‐defined calibration or creating a new two‐
point linear calibration if needed. Use the Set to zero option in Coach 6 to adjust the
zero point of the sensor. The user calibration is stored in non‐volatile user sensor
memory.
2 | ML51m Magnetic Field Sensor User’s Guide
Suggested experiments
This Magnetic Field sensor can be used for:
 Measurements of the magnetic field near a (strong) permanent magnet.
 Measurements of the magnetic field near a current‐carrying wire.
 Measurements of the magnetic field near or inside a coil or solenoid.
 The variation of the field in Helmholtz coils.
Figure 1. Measuring the magnetic field near a permanent magnet.
Magnetic field strength measurement
Magnetic field strength (also known as the magnetic flux density) is a measure of the
force the magnetic field will exert on an electric current or another magnet.
In S.I. units magnetic field strength is expressed in teslas (T). In cgs units magnetic
field strength is expressed in gauss (G).
1 G = 1 x 10‐4 T = 0.1 mT
Below are given magnetic field strength values of exemplary magnetic sources.
Magnetic field strength
in gauss
10‐9 – 10‐8
0.31 ‐ 0.58
25
50
100
2000
15,000 ‐ 30,000
Magnetic field source
The human brain magnetic field
The Earth’s magnetic field on its surface
The Earth's magnetic field in its core
A typical refrigerator magnet
A small iron magnet
A small neodymium‐iron‐boron (NIB) magnet
A medical magnetic resonance imaging electromagnet
ML51m Magnetic Field Sensor User’s Guide | 3
Technical Specifications
Sensor kind
Digital: on‐sensor analog to digital conversion
(14‐bits resolution, communication via I2C)
Measuring range
‐ 1000 .. 3000 gauss
Resolution
Current requirement
Typical 0.244 gauss
Radiometry sensitivity error:
Typical ± 1.5% at full range and temperature of 25°C
Linearity sensitivity error: Typical ±3.5%
Accuracy: Typical ± 5.0%
Typical 27mA at 25°C
Maximum sampling
1000 Hz
Sensor dimensions
Housing: 70 x 21 x 70 mm (W x D x H)
Stainless Steel Probe:
Length: 130mm
Diameter: 7mm
5‐pins mini jack plug
Uncertainty
Connection
Warranty:
The Magnetic Field sensor ML51m is warranted to be free from defects in materials
and workmanship for a period of 12 months from the date of purchase provided that
it has been used under normal laboratory conditions. This warranty does not apply if
the sensor has been damaged by accident or misuse.
Note: This product is to be used for educational purposes only. It is not appropriate
for industrial, medical, research, or commercial applications.
Rev. 17/11/2011
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