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OM1004 ISSUE 20 PAGE 11 OF 30
saturation point. The output will remain at the saturation level if the field is increased
beyond this point. Asymmetric supplies may be used provided that the minimum and
maximum voltages are not exceeded for either polarity.
6.4
SIGNAL/POWER GROUND
The two signal/power ground conductors are connected to a common point within the
sensor and the power supply common (power 0 V) should be connected to only one of
them. The other signal/power ground conductor should be used as the signal output
common (signal 0 V). Each signal is then measured between the signal output
conductor and the signal output common. In this way the signal output common carries
no power supply currents.
The minimum current in the power ground conductor is approximately 19mA and, on long
cables, this will give rise to an appreciable potential difference between the power supply end
and the sensor end of the power ground conductor. The use of separate power and signal
ground conductors will ensure that this voltage is not included in the voltage measured
between the signal output and the signal common.
In order to ensure that the power supply return current does not affect the analog
measurements in any way, the following precautions should be observed:
a. A signal common line, separate from the power return line, must be connected between
the
Mag
-03 magnetic field sensor and any measurement or data acquisition system.
b. If the signal ground line is to constitute a system ground point then a fully floating power
supply must be employed, e.g. a pair of batteries or a fully isolated power supply. A number
of commercially available dc to dc converters fulfil the voltage isolation requirement
adequately. For this arrangement only single ended analog inputs to the data acquisition
system are required for the three axes.
c. If the power supply is to constitute a system ground point then the data acquisition analog
inputs must be of the differential type. Each differential input can then be connected between
the remote end of the signal common line and the individual analog outputs.
d. The above considerations also apply if more than one
Mag
-03 sensor is used.
e. Any data acquisition system analog inputs should ideally have a very high input
impedance but satisfactory performance can be obtained with impedance’s down to 10k
Ω
.
Impedance’s below this should be avoided, particularly where very long cables are used.
f. To obtain optimum performance, additional care should be exercised to avoid ground
currents in the signal leads when using the low noise unit.
When using the
Mag
-03PSU power supply,
Mag
-03DAM data acquisition module or
Mag
-03SCU signal conditioning unit described in Section 4 the above requirements will be
met without further consideration by the user.