ETS-Lindgren HI-4433-STE Electric Field Probe - Manual (Page 20)

20 | Practical Application and Use
In addition to the inputs from the three axes, HI-4433 series probes utilize a
fourth input called the Autozero channel. This is a redundant channel identical to
the three axis channels except that, instead of being driven by a dipole, it is
terminated (in the probe head) by a carbon resistor. This resistor simulates the
zero-bias impedance of the Schottky diode in series with the high resistance feed
line; it is also subject to the same temperature variations as the feed lines of the
other three channels.
Probe Power Supply
A sealed rechargeable 3.6 VDC NiCd battery, which drives both the analog and
digital power supplies, powers HI-4433 series probes; separate power sources
provide isolation between the analog and digital circuitry. With the probe switch
in the ARM position, battery voltage is applied to the power switch, which routes
this voltage to the power control and the switching power supply, enabling the
microprocessor. This power supply does not shut off automatically. Always turn
the power supply off when the probe is not in use.
Application Considerations
Resolution Limitations
Limitations in probe resolution may result in a non-zero reading
when the receiver is zeroed. If this occurs, it does not necessarily
mean either that there is a problem with the receiver or that your
readings are inaccurate. Receiver linearity is specified as + 0.5
dB full scale: in addition, the variance of the A/D converter is + 2
least significant bits. When using the most sensitive range on a
given probe, these specifications create the possibility that, under
zero field conditions, the receiver may display a non-zero value.
Probe Support Structures
It is very important to keep conductive objects away from the HI-
4433. Any such objects in the proximity of the probe may distort
the near field and compromise measurement accuracy. If your
application requires measurements from a fixed position, always
mount the probe on a non-metallic platform, using non-metallic
screws.