Campbell CS110, Инструкция по эксплуатации, Страница: 18 / 86

CS110 Electric Field Meter
8
This charge amplifier input leakage current increases with degradation of insulation
of the sense electrode insulators due to moisture or other surface contamination.
Consequently, the measurement and reporting of I
leak
is useful in determining if or
when insulators should be cleaned.
The reciprocating motion of the CS110 electric field meter is limited to
approximately 5 Hz, which is adequate for lightning hazard warning, where 1 minute
averaged data is often used. For applications desiring > 5 Hz, the CS110
reciprocating electric field meter can be configured as a slow antenna
(MacGorman
and Rust 1998). The shutter would typically be left open indefinitely in slow
antenna mode and resistor R3, depicted in Figure 2, is switched in parallel with Cf
providing a 66 ms decay time constant for the charge amplifier. In the slow
antenna mode, the charge amplifier has a high-pass filter frequency response with
the lower cutoff frequency defined as f
3dB
= (2
⋅π⋅
R
⋅
C)
-1
= 2.4 Hz. In this mode the
instrument is a field change meter and the charge amplifier output can be sampled
by the datalogger as fast as every 20 ms (50 Hz), using 250
μ
s integration
durations for the analogue integrator. Voltage measurements using the 250
μ
s
integration duration for an analogue integrator, result in an upper 3 dB bandwidth
of 1.8 kHz. Detailed information regarding the slow antenna mode of the CS110
is given in Appendix E and Section 8.3.
4. Site Requirements and Recommendations
4.1 Power Requirements
Field mills typically consume many watts of power because their motors are
operated continuously. In the reciprocating approach, the stepper motor is
powered off much of the time, resulting in low power consumption. The current
required by the CS110 powered from 12 V DC is shown in Figure 4. As depicted
in the figure, the average electric field meter current is a function of the desired
measurement rate, which is user-controlled by means of the datalogger program,
making economical remote solar power feasible. Variable sample rates based on
measured results can also be implemented to conserve power in solar powered
applications. For example, the datalogger can be programmed to measure electric
field at a 10-second rate during fair weather conditions, and then automatically
switch to 1-second measurements during threatening conditions. An example
variable sample rate program is given in Appendix F. Figure 4 does not include
the current required for peripheral devices necessary to communicate with the
CS110 site. Like the stepper motor, communication devices that are turned off
when not needed, can offer low average power consumption.