Specifications

BARTINGTON INSTRUMENTS
Page 7 of 12 M2240 ISSUE 1
Using the Mag639
Cabling
It is recommended that the connecting cable to the sensor is an eight-core screened cable. Two cores will
be used for positive and negative power supply lines, three cores for output signals, one core for signal
common and one for power supply ground. The screen should be connected to supply ground at the supply
end only. The capacitance between cores should be less than 200pF per metre. A cable with individually
shielded cores should be considered for long cable applications.
Note: Leads are susceptible to EM interference and should be screened wherever possible.
The length of the cable is limited by the voltage drop in the power supply lines and the capacitance
between the cores. Long cables will limit both the bandwidth and the full-scale range of the Mag639.
Connecting Power
Caution: Check that the polarity of the supply is correct. The power supply should be connected to
the sensor before the supply is energised as this prevents high inrush currents which could cause
damage. Apply the positive and negative supplies simultaneously and avoid leaving the sensor
connected to one polarity only.
Response
The analog output V, for any channel, is proportional to the axial component b of the total field F. If θ is the
angle subtended between the direction of F and sensing axis of the fluxgate element, then:
b = F cosθ and V ∝ F cosθ
Electromagnetic Compatibility
The Mag639 is not shielded for immunity from, or emission of, electromagnetic fields. Any shield placed
around the sensor will limit the bandwidth of the sensor response. The emissions generated are at a low
level with a primary frequency of 32kHz, being the frequency of the energising field of the sensor. The
sensor is required to respond to magnetic fields within the specified frequency band.
The user should ensure that the sensor is not operated in areas where a high electromagnetic field exists,
even if the frequency is above the bandwidth of the sensor, as false information may appear due to
aliasing. This effect is seen in data acquisition systems when the frequency of sampling is lower than the
frequency of the signal which is being sampled. It may produce apparent signals at lower frequencies than
the noise, which may be within the frequency band of the sensor. Similarly, the user should not place the
sensor near to any equipment which may be affected by the fields produced by the sensor excitation.