Campbell Scientific CS110 User Manual

CS110 Electric Field Meter

Revision: 4/12

Copyright © 2005-2012

Campbell Scientific, Inc.

Warranty

“PRODUCTS MANUFACTURED BY CAMPBELL SCIENTIFIC, INC. are
warranted by Campbell Scientific, Inc. (“Campbell”) to be free from defects in
materials and workmanship under normal use and service for twelve (12)
months from date of shipment unless otherwise specified in the corresponding
Campbell product manual. Batteries, fine-wire thermocouples, desiccant, and
other consumables have no warranty. Campbell's obligation under this
warranty is limited to repairing or replacing (at Campbell's option) defective
products, which shall be the sole and exclusive remedy under this warranty.
The customer shall assume all costs of removing, reinstalling, and shipping
defective products to Campbell. Campbell will return such products by surface
carrier prepaid within the continental United States of America. To all other
locations, Campbell will return such products best way CIP (Port of Entry)
INCOTERM® 2010, prepaid. This warranty shall not apply to any Campbell
products which have been subjected to modification, misuse, neglect, improper
service, accidents of nature, or shipping damage. This warranty is in lieu of all
other warranties, expressed or implied. The warranty for installation services
performed by Campbell such as programming to customer specifications,
electrical connections to products manufactured by Campbell, and product
specific training, is part of Campbell’s product warranty. CAMPBELL
EXPRESSLY DISCLAIMS AND EXCLUDES ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR PURPOSE. Campbell is not liable for any special, indirect,
incidental, and/or consequential damages. In no event will CAMPBELL
SCIENTIFIC, INC. have liability in excess of the purchase price for the
CS110. CAMPBELL SCIENTIFIC, INC. does not warrant that the CS110 will
meet customer’s requirements or that its operation will be uninterrupted or
error-free. Atmospheric or local electric field conditions or different site
characteristics may cause false information, late data, or otherwise incomplete
or inaccurate data. Site correction and warning threshold levels are the
responsibility of the user. The user is responsible to set time since a threshold
was passed to clear an alarm, because these threshold levels may vary with
sensitivity to nature of risk (e.g., handling explosives) and cost of disruption
with an alarm (playing golf vs. fueling airplanes). The CS110 only measures
conditions that make lightning more likely. Just as with weather forecasts,
CS110 measurements only help assess the probability of lightning. Lightning
can occur causing personal injury, even death, or damage to property without
any warning from the CS110.”

Assistance

Products may not be returned without prior authorization. The following
contact information is for US and international customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle
repairs for customers within their territories. Please visit

www.campbellsci.com to determine which Campbell Scientific company serves

your country.

To obtain a Returned Materials Authorization (RMA), contact CAMPBELL
SCIENTIFIC, INC., phone [phone]. After an applications engineer
determines the nature of the problem, an RMA number will be issued. Please
write this number clearly on the outside of the shipping container. Campbell
Scientific's shipping address is:

CAMPBELL SCIENTIFIC, INC.
RMA#_____
815 West 1800 North
Logan, Utah 84321-1784

For all returns, the customer must fill out a "Statement of Product Cleanliness
and Decontamination" form and comply with the requirements specified in it.
The form is available from our web site at www.campbellsci.com/repair. A
completed form must be either emailed to [e-mail] or faxed to
[phone]. Campbell Scientific is unable to process any returns until we
receive this form. If the form is not received within three days of product
receipt or is incomplete, the product will be returned to the customer at the
customer's expense. Campbell Scientific reserves the right to refuse service on
products that were exposed to contaminants that may cause health or safety
concerns for our employees.

CS110 Table of Contents

PDF viewers: These page numbers refer to the printed version of this document. Use the
PDF reader bookmarks tab for links to specific sections.

1. General Description.....................................................1

1.1 CS110 Introduction...................................................................................1

1.2 CR1000 Datalogger ..................................................................................2

1.3 Meteorological Inputs...............................................................................2

1.4 Communication and Data Storage ............................................................2

1.5 Digital I/O.................................................................................................3

1.6 Self-Check Features..................................................................................3

2. CS110 Specifications ..................................................4

3. CS110 Measurement Details....................................... 7

4. Site Requirements and Recommendations...............9

4.1 Power Requirements.................................................................................9

4.2 Campbell Scientific, Inc. Power Supplies ..............................................10

4.3 Communication Options.........................................................................10

4.4 Site Recommendations ...........................................................................11

5. Factory Calibration and Site Correction..................11

5.1 Factory Calibration .................................................................................11

5.2 Site Correction........................................................................................14

6. Lightning Warning ..................................................... 19

7. CRBasic Programming.............................................. 21

8. CS110 Measurement Instructions ............................ 25

8.1 CR1000 Measurement Overview............................................................25

8.2 Measuring Electric Field.........................................................................27

8.3 Measuring Electric Field Change ...........................................................27

8.4 Measuring Solar Radiation or Barometric Pressure................................27

8.5 Measuring Air Temperature and Relative Humidity ..............................28

8.6 Measuring Wind Speed and Direction....................................................28

8.7 Measuring Rainfall .................................................................................29

8.8 Measuring Internal Case Humidity.........................................................29

9. PC Software................................................................29

9.1 Quick Start..............................................................................................29

i

CS110 Table of Contents

10. Maintenance .............................................................33

11. References................................................................40

Appendices

A. CS110 Measurement Status Codes ....................... A-1

B. CS110 Accessories ................................................. B-1

10.1 Checking Site Ground Integrity ........................................................... 33

10.2 Corrosion and Rust Inhibitors.............................................................. 33

10.3 Self-Check Features ............................................................................. 35

10.4 Cleaning the CS110 Electrode Head.................................................... 36

10.5 Changing Desiccant ............................................................................. 37

10.6 Checking Shutter/Encoder Alignment ................................................. 39

10.7 Re-Calibration...................................................................................... 40

B.1 Zero Field Cover Plate ........................................................................ B-1

B.2 Upward-Facing Site Calibration Kit.................................................... B-1

B.3 CR1000 Keyboard Display ................................................................. B-1

B.4 Miscellaneous Peripheral Modules...................................................... B-1

C. CS110 Connector Pin-outs .....................................C-1

D. Servicing the CS110................................................ D-1

D.1 Lid Gasket........................................................................................... D-1

D.2 Changing Out the CR1000.................................................................. D-1

D.3 Changing Out Motor Assembly .......................................................... D-2

D.4 Changing Out the CS110 Panel Board Assembly............................... D-2

D.5 Shutter/Encoder Alignment................................................................. D-3

D.6 Motor O-ring Seal ............................................................................... D-6

E. CS110 as a Slow Antenna....................................... E-1

E.1 Response of the CS110 Slow Antenna in the Frequency Domain .......E-1

E.2 Response of the CS110 Slow Antenna in the Time Domain................E-3

E.3 Programming ........................................................................................E-5

E.4 Calibration ............................................................................................E-6

F. Example CRBasic Programs .................................. F-1

G. CS110 2 Meter CM10 Tripod Site ...........................G-1

ii

CS110 Table of Contents

H. Tripod CS110 and StrikeGuard Site....................... H-1

H.1 Tripod CS110 and StrikeGuard .......................................................... H-1

H.1.1 Installation of the Tripod CS110 and StrikeGuard site............. H-2

H.1.2 Determination of Csite .............................................................. H-7

Figures

1. CS110 Electric Field Meter ........................................................................1

2. Charge amplifier circuitry of reciprocating electric field meter .................7

3. Charge amplifier output during an electric field measurement cycle .........8

4. CS110 average current consumption versus measurement interval..........10

5. Parallel-plate electric field meter calibration chamber ..............................12

6. Factory calibration data for CS110 SN: 1026...........................................13

7. NIST calibration certificate ......................................................................14

8. CS110 2 Meter CM10 Tripod Site............................................................15

9. Campbell Scientific, Inc. electric field meter site correction facility........16

10. CS110 attached to upward-facing flush-mounted plate for site

correction ...........................................................................................17

11. Site correction data for CS110 2 Meter CM10 Tripod Site....................18

12. Electric field measured with CS110 during local thunderstorm.............20

13. CS110 stator, shutter and sense electrode...............................................36

14. Inside of CS110 case illustrating bracket for holding desiccant.............38

D-1. Exploded View of CS110 Electric Field Meter................................. D-1

D-2. CS110 Motor Assembly .................................................................... D-5

E-1. CS110 slow antenna frequency response............................................ E-2

E-2. KSC electric field and CS110 slow antenna data................................E-3

E-3. KSC electric field change and CS110 slow antenna data ................... E-4

G-1. CS110 2 Meter CM10 Tripod Site .................................................... G-1

G-2. CS110 on CM10 Tripod Mast ........................................................... G-3

G-3. Earth Grounding ................................................................................ G-4

G-4. Determination of Csite ...................................................................... G-5

H-1. Tripod CS110 and StrikeGuard......................................................... H-1

H-2. CS110 and StrikeGuard on Tripod Mast ........................................... H-3

H-3. Grounding the CS110 Grounding Strap ............................................ H-4

H-4. Grounding the Tripod and Battery .................................................... H-5

H-5. Connections for Combined System ................................................... H-6

H-6. Determination of Csite ...................................................................... H-7

iii

CS110 Table of Contents

iv

CS110 Electric Field Meter

1. General Description

1.1 CS110 Introduction

Case Lid

Atmospheric electric fields have been measured for decades by electric field
meters nicknamed “field mills”. Traditional field mills employ a spinning

meters nicknamed “field mills”. Traditional field mills employ a spinning
metal rotor (vane) electrically connected to Earth ground, placed between the

metal rotor (vane) electrically connected to Earth ground, placed between the
external field and stationary metal sense electrodes. The grounded spinning

external field and stationary metal sense electrodes. The grounded spinning
rotor alternately shields and exposes the sense electrodes from the electric field

rotor alternately shields and exposes the sense electrodes from the electric field
to be measured, resulting in a modulation of the induced charge on the sense

to be measured, resulting in a modulation of the induced charge on the sense
electrodes. Typically, a pair of charge amplifiers converts the modulated

electrodes. Typically, a pair of charge amplifiers converts the modulated
charge into AC voltages that are synchronously rectified and filtered to form a

charge into AC voltages that are synchronously rectified and filtered to form a
low-frequency voltage proportional to the low-frequency (≤10 Hz) electric

low-frequency voltage proportional to the low-frequency (≤10 Hz) electric
field.

field.

Ground Strap

easured for decades by electric field

Reciprocating Shutter

FIGURE 1. CS110 Electric Field Meter

Sealed Connectors

Stator

1

CS110 Electric Field Meter

1.2 CR1000 Datalogger

1.3 Meteorological Inputs

Unlike traditional rotating vane field mills, the CS110 uses a reciprocating
shutter. A stepper motor opens and then closes the reciprocating shutter by 45°
during measurements. The reciprocating shutter is electrically connected to
ground potential by a flexible stainless-steel strap operated below its fatigue
limit, resulting in an ultra-reliable electrical ground connection. The CS110
offers improved dc error performance, as compared with traditional rotating
vane field mills, by utilizing a zero field (closed shutter) reference for each
measurement. Power consumption is also reduced (< 1 Watt for 1
measurement per second) in the CS110 by de-energizing the motor coils in
between measurements.

The CS110 contains an embedded CR1000 datalogger, which provides
measurement and control functions, data processing and storage, a user
interface language (CRBasic™), and flexible communications options.
LoggerNet™ PC software (purchased separately) provides versatile networking
and data collection capabilities. For more details on the CR1000 datalogger
see the CR1000 Measurement and Control System Operator’s Manual.

The CS110 interfaces to various meteorological sensors resulting in an
automated weather station that includes atmospheric electric field. Wind speed
and direction, air temperature and relative humidity, rainfall, solar radiation or
barometric pressure sensors interface directly to the CS110. Measurement
details of the various sensors are given in section 7.

1.4 Communication and Data Storage

The circular RS-232 connector on the underside of the CS110 can be used to
interface directly to RS-232 devices (DTE or DCE), utilizing the CS110
RS-232 cable (CS110CBL1-L).

The circular CS I/O connector on the underside of the CS110 can be used to
interface directly to various Campbell Scientific, Inc. peripherals, utilizing the
CS110 CS I/O cable (CS110CBL2-L). Examples of CS I/O peripherals include
the CR1000 Keyboard Display and the COM220 phone modem.

The DB9 end of CS110 RS-232 cable and CS110 CS I/O cable won’t fit through
the conduit used on some enclosures, whereas the smaller circular end that
connects to the CS110 will.

The embedded CR1000 will have either 2 MB (PN: 18292) or 4 MB (PN:

18293) of battery-backed SRAM and 16K Flash EEPROM. The operating
system and user programs are stored in Flash EEPROM. Memory not used by
the operating system and user program is available for data storage. The size
of available memory can be seen in the Status Table discussed in Appendix B
of the CR1000 manual.

2

1.5 Digital I/O

Three general purpose 0 to 5 V digital I/O lines are available on the CS110
Power cable (CS110CBL3-L) that attaches to the circular power connector on
the underside of the CS110. The blue, yellow, and green wires connect to
control ports C1, C2, and C3 respectively. Using CRBasic, these digital I/O
lines can be used to conditionally turn on alarms, provide an interrupt or pulsed
signal to be measured by the CS110, or as a serial communication port.

1.6 Self-Check Features

The CS110 has been designed to provide reliable electric field measurements
and to minimize and simplify maintenance. The CS110 incorporates extensive
self-checking for each measurement in an effort to identify measurement
problems and reduce or eliminate scheduled maintenance. The status code
returned from each electric field measurement reports on instrument health
along with any measurement problems as described in Appendix A.

For example, insulator leakage current is measured during each electric field
measurement, indicating the cleanliness of electrode insulators. A leakage
current compensation circuit for the charge amplifier input is incorporated in
the CS110 to minimize the effects of insulator leakage current on measured
results (Patent pending). A status code indicating excessive leakage current is
returned if the measured input leakage current exceeds the compensation range
due to insulator cleanliness problems.

CS110 Electric Field Meter

A relative humidity sensor is included inside the CS110 case to provide
information on when case desiccant should be changed. The CS110 also
provides measurement of the battery input voltage in order to monitor the input
power to the instrument. Section 7 discusses CS110 electric field measurement
details. CS110 maintenance details are discussed in Section 10.

3

CS110 Electric Field Meter

2. CS110 Specifications

Electric Field Measurement Performance:

Parallel-Plate Configuration

Accuracy

Measurement

3

(V m-1)

Range

±1% of reading + 60 V m

Resolution

(V m-1)

Sensitivity

(µV/V m

1

)

-1

offset1

Noise

-

(V m

-1

RMS)

±(0 to 21,000) 3 12 4.0

±(21,000 to 212,000) 30 118 18.0

2 m CM10 Tripod Configuration2

Accuracy

Measurement

3

(V m-1)

Range

±5% of reading + 8 V m

Resolution

(V m-1)

Sensitivity

(µV/V m

1

)

-1

offset1

Noise

-

(V m

-1

RMS)

±(0 to 2,200) 0.32 1.2 0.42

±(2,200 to 22,300) 3.2 13 1.9

1

Typical offset for clean electrodes is ≤ |30 V m-1| for the
parallel-plate configuration, which is reduced by the field
enhancement factor for typical inverted and elevated mounting
configurations.

4

2

Field enhancement due to typical inverted and elevated
mounting requires additional site correction, estimated at ±5%
accuracy when done in appropriate high field conditions.
Practical outdoor CS110 electric field measurement accuracy is
estimated at ±5% of reading + 8 V m

-1

for the CS110 2 Meter

CM10 Tripod Site.

3

The CS110 incorporates automatic gain ranging between two
input ranges. The measurement is first tried on the lowest input
range. If the signal is too large for the lowest range, the larger
range is used.

Standard Mounting: 2 m height on a CM10 tripod mast

Site Correction: Site correction factors available for several standard

mounting configurations

CS110 Electric Field Meter

Sample
(Measurement) Rate: Programmable sample rate up to 5 samples per

second, variable sample rates possible. Variable
example: sample every 10 seconds until field
exceeds threshold then sample once a second until
field returns to normal.

Power Requirements: 11 to 16 Vdc; peak-current demand is 750 mA

during motor operation.

7 mA @ 12 V = 0.08 W average power

consumption at 1 sample per 10 seconds

60 mA @ 12 V = 0.7 W average power

consumption at 1 sample per second

120 mA @ 12 V = 1.4 W average power

consumption at 2 samples per second

300 mA @ 12 V = 3.6 W average power

consumption at 5 samples per second

Communication: 1 RS-232 port; 1 CS I/O port used to interface with

our peripherals such as a COM320 Voice Modem;
digital control ports 1, 2, and 3 for alarm, SDI-12
communications, or asynchronous communications

Baud Rates: Selectable from 300 to 115,200 bps

ASCII Protocol: One start bit, one stop bit, eight data bits, no parity

Lightning Protection: Multi-stage transient protection on all extenal

interfaces

CE Compliance: Standards to which conformity is declared—BS

EN61326:2002

Connectors/
Compatible Sensors: Connector Label Compatible Sensors

1

Temp/RH: HC2S3-L, HMP60-L (choose the -C cable

termination option for these sensors)

Wind: 05103-LC, 05106-LC, 05305-LC, 034B-LC,

03001-LC

Solar: LI200X-LC pyranometer, CS100 barometer or

CS106 barometer (the barometer attaches to the
CS110 via the 17640 cable; they must be housed in
a separate enclosure such as the ENC100)

Rain: CS700-LC, TB4-LC, TE525-LC, TE525WS-LC,

1

One sensor per connector

Programmability: CRBasic

TE525MM-LC

TM

programming allows the selection of
sample rate, data processing and storage options
and setting output ports based on alarm conditions.
LoggerNet

TM

includes the CRBasic editor and

compiler.

5

CS110 Electric Field Meter

Rugged Construction: Ultra-reliable metallic ground connection to

reciprocating shutter (no wiping contact), brushless
stepper motor, powder-coated aluminum case,
Teflon insulators, and electro-polished 316L
stainless steel used for corrosion protection of
critical exposed metallic parts

Easy Maintenance: The stator is easily removed for cleaning (proper

cleaning does not invalidate calibration).
Instrument self-checking allows maintenance to be
performed on an as needed basis. The self-checking
also monitors internal humidity, insulator
cleanliness, and power supply voltage, and verifies
that CS110 components such as the charge
amplifier and shutter open/close are functioning
properly.

Operating
Temperature Range: -25° to 50°C standard, -40° to +85°C optional

RH Range: 0 to 100% RH

Dimensions: 15.2 x 15.2 x 43.2 cm (6 x 6 x 17 in)

Mounting: Vertical pipe 1.91 to 6.35 cm OD (0.75 to 2.5 in)

Weight: 4 kg (9 lb)

6

3. CS110 Measurement Details

The charge amplifier circuitry of the reciprocating electric field meter is
depicted in Figure 2. Induced charge on the sense electrode results in the
operational amplifier placing charge on the feedback capacitor C in order to
restore the sense electrode to virtual ground.

CS110 Electric Field Meter

FIGURE 2. Charge amplifier circuitry of reciprocating electric field

meter

The charge amplifier output during a measurement cycle of the reciprocating
electric field meter is illustrated in Figure 3.

7

CS110 Electric Field Meter

160

FIGURE 3. Charge amplifier output during an electric field

measurement cycle

Offset voltages Voff1 and Voff2 are zero field reference measurements made
when the shutter is closed, and utilized to accurately estimate voltage ΔV when
the shutter is completely open. Electronic offset voltages, surface potentials
between various metallic parts and leakage currents on the charge amplifier input
result in non-zero values of Voff1 and Voff2. An electronic reset of the charge
amplifier is performed prior to the measure of Voff1 to keep the charge amplifier
output near zero volts when the shutter closed. The measured electric field E, as
determined from the charge amplifier output is as follows:

E = k⋅ΔV = k⋅[Vopen – (Voff1 + Voff2)/2] (eq. 1)

Where k is a constant determined by electrode geometry and electronic gain.

The resulting algorithm effectively eliminates measurement error sources that vary
slowly with respect to the time between zero field reference measurements, which
is approximately 140 ms. Measurement noise due to 50 or 60 Hz AC power can
be suppressed by utilizing the 50 Hz or 60 Hz noise rejection measurement
capability of the datalogger.

Current source Ileak in Figure 2 represents leakage currents across the Teflon
insulators supporting the sense electrode, along with the input bias current of the
operational amplifier. Deleterious effects of Ileak are compensated for in the
determination of ΔV as given in (eq. 1). However, it is desirable to minimize the
difference between Voff1 and Voff2 in order to preserve dynamic range for large
magnitude Vopen voltages. Hence a leakage-current compensation circuit is
utilized to generate the current Icomp, illustrated in Figure 2, such that Icomp =
Ileak. The leakage-current compensation algorithm determines Icomp for the
present measurement based on Ileak from the previous measurement, which is
determined as follows:

8

CS110 Electric Field Meter

Ileak = Cf·(Voff1 – Voff2)/ΔT + Icomp (eq. 2)

Where Cf is the value of feedback capacitor used in the charge amplifier, and
Icomp is the leakage current compensation value implemented during the
measurement.

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 Ileak 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 high­pass filter frequency response with the lower cutoff frequency defined as f
(2⋅π⋅R⋅C)
the charge amplifier output can be sampled by the datalogger as fast as every
20 ms (50 Hz), using 250 μs integration durations for the analog integrator.
Voltage measurements using the 250 μs integration duration for an analog
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.

-1

= 2.4 Hz. In this mode the instrument is a field change meter and

3dB

=

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.

9

CS110 Electric Field Meter

1000

100

10

Average Current (mA) @ 12 V

1

0.1 1 10 100

Measurement Interval (Seconds)

FIGURE 4. CS110 average current consumption versus measurement

interval

The CS110 requires 11 V to 16 Vdc with a peak current demand of 750 mA
during motor operation. The CS110 Power Cable (pn 16965) is used to
connect the dc power supply to the CS110. The recommended maximum
length on the CS110 Power Cable (CS110CBL3-L) is 50 feet. The CS110 is
protected against accidental reversal of the positive and ground leads from the
dc power supply. Transient protection is also included on the power supply
inputs. DC input voltages in excess of 18 V may damage the CS110.

4.2 Campbell Scientific, Inc. Power Supplies

The PS100 provides a 12 Vdc, 7.0 Ahr rechargeable power supply for the
CS110 and peripherals. The CH100 is a charging regulator for 12 V
rechargeable batteries that is commonly used with the larger 12 amp hour
(BP12) and 24 amp hour (BP24) Battery Packs. The rechargeable battery can
be trickle-charged from an ac power wall charger. The PN: 9591 wall charger
accepts 110 Vac while the PN: 14014 accepts 90 to 264 Vac. Charging power
can also come from a 17 – 28 VDC input such as a solar panel. Depending on
power requirements, 10 watt or 20 watt solar panels (SP10 or SP20) are
available.

4.3 Communication Options

10

The circular RS-232 connector on the underside of the CS110 can be used to
interface directly to RS-232 devices (DB-9), utilizing the CS110 RS-232 cable
(CS110CBL1-L).

The circular CS I/O connector on the underside of the CS110 can be used to
interface directly to various Campbell Scientific, Inc. peripherals, utilizing the

CS110 CS I/O cable (CS110CBL2-L). Examples of CS I/O peripherals include
the CR1000 Keyboard Display and the COM220 phone modem.

The CS110 also offers SDI-12 communication or SDM (Synchronous Device
for Measurement) control capability utilizing the CR1000 control ports
available through the CS110 POWER CABLE (CS110CBL3-L).

4.4 Site Recommendations

Many factors can distort and/or change the electric field at a given sight. For
example, vegetation growth can reduce the effective height of an elevated
instrument above the ground and can created unwanted space-charge due to
corona discharge. Gravel rings or concrete pads around a given site are
recommended to prevent changes in effective instrument height due to
vegetation growth. Electric field meters used for lightning warning at Kennedy
Space Center use a 25-foot radius gravel ring around each electric field meter
[LPLWS].

Animals and people within the vicinity of an electric field meter can
significantly alter the measurements. Fencing off a given site may be best for
some applications. However, installing a small metal fence around an electric
field meter site may result in corruption of measurements at large electric fields
because of corona discharge from sharp metal points on the fence.

CS110 Electric Field Meter

Aerosols, dust, and automobile exhaust should be considered when selecting an
electric field meter site, as they can affect the local electric field.

In theory, the effects of tall nearby objects can be accounted for in site
correction. Yet, because of possible corona current along with general field
distortion, it is recommended that electric field meter sites should not be
located near tall objects. Kennedy Space Center site requirements stipulate
having no objects protruding higher than 18° above the horizon, as seen from
the ground at the electric field meter location [LPLWS]. Roof mounted
electric field measurements are practical if a site correction can be done to
account for field distortions.

Also a good Earth ground connection to the CS110 and associated mounting
hardware is necessary to make a given site appear as a vertical extension of the
Earth ground. It is recommended that the integrity of this Earth Ground
connection be checked periodically by verifying that the resistance of the stator
to Earth Ground rod is <1 Ω.

Although the list of factors that can impair electric field measurements is long,
experience has shown that useful electric field measurements can be made by
paying careful attention to the above mentioned details.

5. Factory Calibration and Site Correction

5.1 Factory Calibration

Electric field meters are typically factory calibrated using a parallel plate
method, where a uniform electric field is developed by applying a known
voltage between parallel conductive plates. The large hexagonal parallel plate
electric field calibrator illustrated in Figure 5 is used for factory calibration of
the CS110 Electric Field Meter. The large physical size was incorporated to

11

CS110 Electric Field Meter

minimize non-ideal fringing effects. Sharp corners were avoided in order to
prevent corona discharge. All metal parts of the calibrator are manufactured
from stainless steel, and the inside surfaces are polished to reduce the surface
charges in order to provide a stable zero electric field. All outer surfaces are
electrically connected and tied to Earth ground while the insulated inner plate
is driven by a high voltage amplifier. The high-voltage amplifier is calibrated
out-of-house yearly against a reference that is traceable to the National Institute
of Standards and Technology (NIST).

12

FIGURE 5. Parallel-plate electric field meter calibration chamber

Each CS110 is factory calibrated in the parallel plate calibration fixture
depicted in Figure 5. A linear fit of the calibration data results in a calibration
equation in slope-intercept form expressed as

E = M

The multiplier M

parallel_plate

is a function of the CS110 electrode dimensions and

parallel_plate

⋅V + O

parallel_plate

the feedback capacitor in the charge amplifier. The offset term O

(eq. 3).

parallel_plate

is
due to unwanted surface charges residing on non-conductive deposits on the
electrodes. The electric field offset of an instrument varies over time because

CS110 Electric Field Meter

of variations in surface cleanliness along with charging and discharging
processes. Polished 316-L stainless-steel is used for critical electrode surfaces
on the CS110 to minimize unwanted surface charges. CS110s with clean
electrodes have been found to display electric field offsets <⏐30 V/m⏐, which
has negligible effect on the determination of M

parallel_plate

because of the ±15

kV/m range of electric fields used during factory calibration. Neglecting
O

parallel_plate

results in the simplified parallel-plate calibration equation

E = M

parallel_plate

The estimated measurement accuracy of M

⋅V (eq. 4).

parallel_plate

for the CS110 calibrated in

the parallel plate electric field calibrator illustrated in Figure 5 is ± 1 %. The
electric field offset of the CS110 can be measured by covering the stator with a
clean Zero Electric Field Cover (PN: 17642). If the resulting zero field reading
with the zero field cover exceeds an absolute value of 60 V/m then cleaning of
electrodes in the CS110 is suggested. The factory calibration data for a typical
CS110 factory calibration and resulting determination of M

parallel_plate

= 84.32

V/m⋅mV (Volts/meter⋅millivolt) is illustrated in Figure 6.

20000

y = 84.324x + 26.258

2

= 1

15000

10000

5000

0

-200 -150 -100 -50 0 50 100 150 200 250

R

Applied Electric Field (V/m)

-5000

-10000

-15000

-20000

Charge Amplifier Output Voltage (mV)

FIGURE 6. Factory calibration data for CS110 SN: 1026

13

CS110 Electric Field Meter

14

FIGURE 7. NIST calibration certificate

NOTE

Careful removal and replacement of the stator on the CS110 does
not invalidate the factory derived M
However, switching stators with another unit or accidentally
bending the stator, shutter or sense electrodes invalidates the
factory parallel-plate calibration because of possible electrode
dimensional changes.

5.2 Site Correction

As previously mentioned, each CS110 is factory calibrated in a parallel plate
calibration fixture resulting in calibration equation 4. However, when
monitoring the Earth’s electric field, equation 4 is valid only if the instrument
aperture is mounted flush with the Earth’s surface and upward-facing. Yet for
permanent outdoor measurements of electric field, a flush-mounted and
upward-facing orientation is problematic because of dirt, bird droppings, rain,
etc., collecting on the sense electrodes and fouling the measurement.

parallel_plate

of a given unit.

CS110 Electric Field Meter

Consequently, a downward facing and elevated configuration as illustrated in
Figure 8 is recommended for long-term field applications.

FIGURE 8. CS110 2 Meter CM10 Tripod Site

Inverting the CS110 reduces the effective gain while elevating it’s height
above ground enhances the gain, with respect to an ideal upward-facing flush­mounted geometry. It should be mentioned that this gain enhancement reduces
the effect of unwanted electrical field offsets. A site correction factor C
necessary to correct M

parallel_plate

[McGorman and Rust]. The corrected multiplier M

M

In equation 5, M
site, whereas C

parallel_plate

is unique for each given site, yet independent of the

site

particular CS110 used at the site. C

for non flush-mounted configurations

becomes as follows:

corrected

= C

corrected

site⋅Mparallel_plate

is unique for each CS110, yet independent of a given

is typically determined by using a flush-

site

is

site

(Eq. 5).

mounted upward-facing unit in the vicinity of the site needing correction.
Campbell Scientific, Inc. developed the site correction facility illustrated in
Figure 9 to determine C

for various site configurations.

site

15

CS110 Electric Field Meter

FIGURE 9. Campbell Scientific, Inc. electric field meter site correction

facility

16

CS110 Electric Field Meter

An upward-facing calibration kit (PN: 17579) was developed to hold the
CS110 in a flush-mounted upward-facing position, as illustrated in Figure 10.

NOTE

FIGURE 10. CS110 attached to upward-facing flush-mounted plate for

site correction

Both the upward-facing and the inverted and elevated unit need
to be electrically connected to Earth potential. This can best be
accomplished by a grounding rod and wire connected to ground
lugs provided on both the upward-facing plate and on the
mounting bracket on the standard CS110.

Ideally, site correction should be done in the absence of precipitation, and
during the presence of slowly varying electric fields of bipolar polarity and
magnitudes large enough to make instrument offset errors negligible. These
conditions may be infrequent in practice, making site correction using a flush­mounted upward-facing unit somewhat challenging. Falling precipitation
along with blowing dirt can result in questionable measurements by an
exposed, upward-facing unit. Cleaning of the electrodes of an upward-facing
unit is recommended after it has been exposed to blowing dust and/or falling
precipitation. The measurement of meteorological parameters such as rainfall,
along with the averaging and data storage capability of the CS110 can be

17

CS110 Electric Field Meter

utilized to autonomously measure, process and store data to aid in site
correction.

Campbell Scientific, Inc. has performed a site correction on the CS110 2 Meter
CM10 Tripod Site described in Appendix G. The collected data between the
upward-facing unit and a downward facing CS110 2 Meter CM10 Tripod Site
is illustrated in Fig 10. A best-fit line computed from the data resulted in C

site

= 0.105 ± 4%, which is valid for users at other sites who use the same site
dimensions on level terrain clear of vegetation. Dimensional details of the 2
meter standard meteorological site are described in Appendix F.

10/02/05 Site Correction of CS110 2 Meter CM10 Tripod Site

-80000 -60000 -40000 -20000 0 20000 40000 60000 80000

Mparallel_plate = 87.6 volt/meter*millivolt

10/02/05 Site Correction of CS110 2 Meter CM10 Tripod Site

Results indicate Csite = 0.105.

Results indicate Csite = 0.105.

8000

y = 0.1051x - 35.664

6000

4000

2000

0

-2000

-4000

-6000

2

= 0.9996

R

Mparallel_plate = 87.6 volt/meter*millivolt

Electric Field (volt/meter for Upward Facing CS110 SN:1022

Electric Field (volt/meter) for Upward Facing CS110 SN:1022

Uncorrected (Csite = 1) Electric Field (volt/meter) for 2 Meter Mounted CS110 on CM10

Uncorrected (Csite = 1) Electric Field (volt/meter) for 2 Meter Mounted CS110 on CM10

Tripod. SN: 1023 (Mparallel_Plate = 81.77 volt/meter*millivolt)

Tripod. SN: 1023 Mparallel_Plate = 81.77 volt/meter*millivolt

-8000

-10000

18

FIGURE 11. Site correction data for CS110 2 Meter CM10 Tripod Site

The user is responsible for determining if a CS110 site is representative of
the CS110 2 Meter CM10 Tripod Site, and if not, for determining the
appropriate site correction.

The atmospheric electric field at the Earth’s surface during fair weather
conditions is on the order of –100 V/m; the negative sign indicating that the
electrostatic force on a positive charge is directed downward to the Earth’s
surface [McGorman and Rust],[Rakov and Uman]. Ballpark site corrections are
sometimes computed in fair weather conditions by assuming a -100 V/m fair
weather field. The accuracy of a fair weather site correction is questionable
because local conditions may result in a fair weather field significantly different
(>100%) from –100 V/m. Also, the unknown electric field offset may be
significant when calibrating at –100 V/m. This offset can be measured by

covering the stator with a clean Zero Electric Field Cover (PN: 17642). Fair
weather field site correction is not recommended for lightning warning
applications because of the relatively poor accuracy in determining Csite.

6. Lightning Warning

Lightning warning devices fall into two classes: lightning detectors and electric
field monitors. Stand-alone lightning detectors provide warning based on
nearby discharges, but give no warning until a detectable discharge occurs.
Electric field monitors measure the atmospheric electric field, indicating the
presence of nearby electrified clouds capable of producing lightning
discharges. Consequently, electric field monitors can give warning at the
beginning of storms prior to hazardous discharges. Both lightning detectors
and electric field monitors are employed in high-risk applications.

Lightning safety guidelines based on human observations exist and should
not be ignored simply because of the presence of sensitive electronic
instrumentation. The NOAA 30/30 rule suggests seeking shelter if thunder is

heard within 30 seconds of a lightning flash (approximately 6 miles), and
remaining in a sheltered area for 30 minutes after the last lightning or thunder
before resuming outdoor activities [NOAA].

CS110 Electric Field Meter

It should be noted that no method of lightning warning completely
eliminates the risks associated with lightning. As mentioned, lightning

detectors give no warning until a detectable discharge has occurred.
Atmospheric electric field yields warning prior to the “first strike” for storms
developing overhead, along with some indication of the end of a thunderstorm.
Yet there are occurrences of cloud-to-ground lightning discharges striking the
ground several miles away from the electrified cloud where the discharge
initiated [NOAA]. Electric field monitors may give no practical warning in
these instances because the electric field in the vicinity of the strike point may
not indicate hazardous levels until milliseconds before the strike.
Consequently, while lightning warning systems can greatly reduce the

probability of death or injury from lightning discharges, they cannot
reduce this probability to zero.

19