CS115
Barometric Pressure Sensor
3/03
C o p y r i g h t ( c ) 2 0 0 2 - 2 0 0 3
C a m p b e l l S c i e n t i f i c , I n c .
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CS115 Table of Contents
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1. Introduction.................................................................1
2. Specifications .............................................................2
2.1 Performance..............................................................................................2
2.2 Electrical...................................................................................................2
2.3 Physical.....................................................................................................2
3. Installation...................................................................3
3.1 Venting and Condensation........................................................................3
3.2 Mounting...................................................................................................3
3.3 Jumper Settings.........................................................................................4
4. Wiring ..........................................................................5
5. Programming ..............................................................5
5.1 Period Averaging Measurement Examples ...............................................7
5.1.1 Period Averaging Measurement Example for CR10(X)..................7
5.1.2 Period Averaging Measurement Example for CR10(X) in a Slow
Executing Program ....................................................................8
5.1.3 Period Averaging Measurement Example for CR23X ....................9
5.1.4 Period Averaging Measurement Example for CR5000 in a Fast
Executing Program at 10 Hz....................................................11
5.2 Pulse Count Measurement Example........................................................12
5.21 Pulse Count Measurement Example for 21X .................................12
5.3 Output Resolution...................................................................................13
6. Correcting Pressure to Sea Level............................13
7. Maintenance and Calibration ...................................14
Figures
3-1 Mounting CS115.......................................................................................3
3-2 Jumper Settings on CS115........................................................................4
Tables
4-1 Wiring for Example Programs..................................................................5
5-1 Conversion Factors for Alternative Pressure Units...................................6
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CS115 Barometric Pressure Sensor
The CS115 Barometric Pressure Sensor uses the resonant silicon technology pressure
sensor developed by Druck. The sensor outputs a variable frequency which can be
measured using the datalogger's period averaging instruction or pulse count instruction.
The entire process is essentially digital from sensor element to datalogger, ensuring the
highest precision and most accurate reading possible.
1. Introduction
The sensor comprises two elements, one acting as a pressure sensitive
diaphragm and the other acting as a resonator. Pressure variations deflect the
sensitive diaphragm and change the sensor’s resonant frequency. The resonant
frequency is measured, corrected for the effects of temperature and non-
linearity, and then output as a frequency signal. The sensor is characterized
over the full temperature and pressure range, and the corrections are stored in
the sensor's non-volatile memory. It can be operated in a triggered or
continuous mode. In the triggered mode the datalogger switches 12 VDC
power to the barometer before the measurement. The datalogger then powers
down the barometer after the measurements to conserve power.
1
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CS115 Barometric Pressure Sensor
2. Specifications
2.1 Performance
Measurement Range:
600 mb to 1100 mb (hPa)
Operating Temperature Range: -40°C to +60°C
Humidity Range:
Media Compatibility:
at 20°C
non-condensing
non-corrosive gas
±0.3 mb
-10°C to +50°C
-20°C to +60°C
-40°C to +60°C
Long-term Stability:
Overpressure Limit:
±0.5 mb
±1.5 mb
±2.0 mb
<0.11 mb per year (100 ppm)
1375 mb
2.2 Electrical
Supply Voltage:
9.5 V to 24 VDC
Current Consumption:
Output Frequency:
Frequency Output:
External Trigger Voltages:
8 mA nominal
600 Hz to 1100 Hz
-2.5 to +2.5 VDC zero-crossing square wave
ON 1 to 24 VDC
OFF 0 VDC
Warm-up Time:
EMC Compatibility:
<2 seconds (-40°C to +60°C)
Emissions – BS EN50081-1
Immunity – BS EN61000-6-2
2.3 Physical
Dimensions (Main Box):
2.36” x 2.36” x 1.15”
(6.0 cm x 6.0 cm x 2.9 cm)
4.4 oz (125 g)
Weight:
Mounting Hole Centers:
Pressure Connector:
3 inches (7.62 cm)
0.16” (0.4 cm) barbed hose
The black outer jacket of the cable is Santoprene® rubber. This
compound was chosen for its resistance to temperature extremes,
moisture, and UV degradation. However, this jacket will support
combustion in air. It is rated as slow burning when tested
according to U.L. 94 H.B. and will pass FMVSS302. Local fire
codes may preclude its use inside buildings.
NOTE
1 Non-linearity, hysteresis, and repeatability over calibrated temperature range
2
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CS115 Barometric Pressure Sensor
3. Installation
3.1 Venting and Condensation
To prevent condensation, install the sensor in an environmentally protected
enclosure, complete with desiccant which should be changed at regular
intervals. As the sensor must detect the external ambient pressure the enclosure
must not be ‘hermetically sealed’.
Failure to protect the sensor from condensation may result
in permanent damage.
CAUTION
NOTE
If it is necessary to make a vent hole on the outer wall of an
enclosure, do not make the hole on one of the vertical side walls,
as wind blowing around it can cause transient changes in
pressure.
3.2 Mounting
The mounting holes for the sensor are one-inch-centered, and will mount
directly onto the holes on the backplates of the Campbell Scientific enclosures.
Mount the sensor with the pneumatic connector pointing vertically downwards
to prevent condensation collecting in the pressure cavity, and also to ensure
that water cannot enter the sensor.
FIGURE 3-1. Mounting CS115
3
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CS115 Barometric Pressure Sensor
As you mount the sensor onto the backplate of the enclosure, place the fork lug
under the mounting screw to accomplish the proper grounding of the sensor as
shown in Figure 3-1.
3.3 Jumper Settings
The CS115 has two operating modes, ‘continuous’ and ‘triggered’. It is normally
shipped in the ‘triggered’ mode, in which the unit is turned on and off by applying
signal to the blue wire (EXT. TRIG.) using a datalogger’s control port. In this
mode, power consumption is minimized, but the sensor is subject to a 2-second
‘warm-up’ delay after it is turned on. You can also configure the unit for the
‘continuous’ mode to avoid the need for the delay, in which the sensor is powered
on continuously. This can be achieved either by connecting the blue wire (EXT.
TRIG.) to a continuous 1 to 24 VDC supply (to 5 V or 12 V channel of the
datalogger) or by changing the jumper position connecting the pins on the circuit
board. See Figure 3-2 below.
Jumper (blue link) –
Position A = continuous mode
Position B = triggered mode
A
B
FIGURE 3-2. Jumper Settings on CS115
4
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CS115 Barometric Pressure Sensor
4. Wiring
The CS115 wiring instructions for the example programs are shown in
Table 4-1. For dataloggers CR500, CR510, CR10(X), CR23X, and CR5000,
analog channel is used for period averaging measurement. For CR7, 21X and
CR9000 pulse channel is used for pulse count measurement.
TABLE 4-1. Wiring for Example Programs
Wire Color
Green
Red
Description
CR10(X)
SE6
12V
G
CR23X
SE24
12V
21X
P1
CR5000
SE33
12V
Frequency Out
Supply (12Vdc)
Power Ground
Signal Ground
External Trigger
Shield
12V
Black
G
G
Yellow
Blue
AG
C8
C1
G
C6
C1
G
Clear
G
5. Programming
There are two ways to measure the output of the CS115. The preferred way is
to use the period averaging instruction available with the CR500, CR510,
CR10(X), CR23X and CR5000 dataloggers. This instruction determines the
period of the output signal averaged over a user-specified number of cycles and
outputs it in kHz.
If you have a datalogger that does not support the period averaging instruction
(e.g., 21X, CR7 or CR9000), a pulse count instruction can be used to measure
the CS115.
Atmospheric pressure changes little with time. In most weather station
applications measuring pressure once an hour is adequate.
In Example 1, the datalogger turns on the CS115 one minute before the top of
the hour with a control port. As in the example, the execution interval must be
one minute or less. The datalogger measures the CS115 on the hour, and then it
turns the CS115 off.
In Example 2, the CS115 is measured every execution interval. The datalogger
turns the CS115 on and waits two seconds for it to warm up before the
measurement is made. The execution interval must be long enough to
accommodate the two-second warm-up delay plus all the other measurements
and processing instructions in the program.
Example 3 resembles Example 1 in every way, but it is for the CR23X.
In Example 4, the CR5000 measures the CS115 once an hour in a program that
runs at 10 Hz. With the CR5000, the period averaging instruction has to be
executed every scan and cannot be inside the “If” statement. The measured
value, therefore, is first written into a temporary variable called "CS115_Freq".
5
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CS115 Barometric Pressure Sensor
Once the CS115 is turned on one minute before every hour, and the correct
measurement is made, it is then copied into the current variable called
"Pressure". The sensor is then turned off immediately following the
measurement. In this example, the CR5000 measures the CS115 once every
hour while measuring other sensors at 10 Hz.
In Example 5, the 21X turns on the CS115 one minute before the top of the
hour, and on the hour it measures the CS115 using the pulse count instruction.
The execution interval should be set at 1 second, and the configuration code for
Pulse instruction (P3) should be set at 24, Low Level AC, 16-bit, Output in Hz.
When this option is selected, two adjacent 8-bit pulse counters (Pulse Input
channels 1 and 2) are combined into one input channel (Pulse Input channel 1)
to form a 16-bit accumulator. Therefore, Pulse Input channel 2 cannot be used.
You can also choose to use Pulse Input channel 3, in which case Pulse Input
channels 4 will be combined with Pulse Input channel 3 to form a 16-bit
accumulator. In this mode, the 21X’s execution interval must be less than one
minute. If the execution interval is longer than one minute, you will get an
error, because the 16-bit pulse accumulator will overflow counting the signal
from the CS115 when it outputs close to 1100 Hz (1100 mb of barometric
pressure).
In the example programs above, the pressure is reported in millibars (mb). To
report pressure in different units, multiply the measured pressure by the
appropriate conversion factor using the P37 (Z=X*F) instruction for the
CR500, CR510, CR10(X), CR23X, 21X and CR7, or by adding an expression
for the CR5000 and CR9000. See Table 5-1 below for conversion factors.
TABLE 5-1. Conversion Factors for
Alternative Pressure Units
To Find
hPa
Multiply by
1.0
kPa
0.1
mm of Hg
in of Hg
psi
0.75006
0.02953
0.0145
0.00099
0.75006
atm
torr
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CS115 Barometric Pressure Sensor
5.1 Period Averaging Measurement Examples
5.1.1 Period Averaging Measurement Example for CR10(X)
EXAMPLE 1. Sample Program for CR10(X)
;{CR10X}
;
*Table 1 Program
01: 1
Execution Interval (seconds)
;Turn on CS115 one minute before the hour
;
1: If time is (P92)
1: 59
2: 60
3: 48*
Minutes (Seconds --) into a
Interval (same units as above)
Set Port 8* High
;Measure CS115 at the top of the hour
;
2: If time is (P92)
1:
2: 60
3: 30
0
Minutes (Seconds --) into a
Interval (same units as above)
Then Do
3: Period Average (SE) (P27)
1:
1
Reps
2: 14
3: 6*
4: 10
200 kHz Max Freq @ 2 V Peak to Peak, Freq Output
SE Channel
No. of Cycles
5:
5
Timeout (units = 0.01 seconds)
6: 1*
7: 1000
8: 0.0
Loc [ P_mb
Mult
Offset
]
;Turn off CS115
;
4: Do (P86)
1: 58*
Set Port 8* Low
5: End (P95)
6: If time is (P92)
1:
2: 60
3: 10
0
Minutes (Seconds --) into a
Interval (same units as above)
Set Output Flag High (Flag 0)
7: Real Time (P77)
1: 0110
Day,Hour/Minute (midnight = 0000)
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CS115 Barometric Pressure Sensor
8: Sample (P70)
1:
1
Reps
2: 1*
Loc [ P_mb
]
*Table 2 Program
02: 0.0000
Execution Interval (seconds)
*Table 3 Subroutines
End Program
-Input Locations-
1 P_mb
* Proper entries will vary with program and datalogger channel, and input location assignments.
5.1.2 Period Averaging Measurement Example for CR10(X) in a Slow
Executing Program
EXAMPLE 2. Sample Program for CR10(X)
;{CR10X}
;
*Table 1 Program
01: 10
Execution Interval (seconds)
Set Port 8* High
;Turn on CS115
;
1: Do (P86)
1: 48*
;Give 2 second delay for CS115 to settle
;
2: Excitation with Delay (P22)
1:
2:
1
0
Ex Channel
Delay W/Ex (0.01 sec units)
Delay After Ex (0.01 sec units)
mV Excitation
3: 200
4:
0
3: Period Average (SE) (P27)
1:
1
Reps
2: 14
3: 6*
4: 10
200 kHz Max Freq @ 2 V Peak to Peak, Freq Output
SE Channel
No. of Cycles
5:
5
Timeout (units = 0.01 seconds)
6: 1*
7: 1000
8: 0.0
Loc [ P_mb
Mult
Offset
]
8
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CS115 Barometric Pressure Sensor
;Turn off CS115
;
4: Do (P86)
1: 58*
Set Port 8* Low
5: If time is (P92)
1:
2: 60
3: 10
0
Minutes (Seconds --) into a
Interval (same units as above)
Set Output Flag High (Flag 0)
6: Real Time (P77)
1: 0110
Day,Hour/Minute (midnight = 0000)
Reps
7: Sample (P70)
1:
1
2: 1*
Loc [ P_mb
]
*Table 2 Program
02: 0.0000
Execution Interval (seconds)
*Table 3 Subroutines
End Program
-Input Locations-
1 P_mb
* Proper entries will vary with program and datalogger channel, and input location assignments.
5.1.3 Period Averaging Measurement Example for CR23X
EXAMPLE 3. Sample Program for CR23X
;{CR23X}
;
*Table 1 Program
01: 1
Execution Interval (seconds)
;Turn on CS115 one minute before the hour
;
1: If time is (P92)
1: 59
2: 60
3: 41*
Minutes (Seconds --) into a
Interval (same units as above)
Set Port 1* High
;Measure CS115 at the top of the hour
;
2: If time is (P92)
1:
2: 60
3: 30
0
Minutes (Seconds --) into a
Interval (same units as above)
Then Do
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CS115 Barometric Pressure Sensor
3: Period Average (SE) (P27)
1:
1
Reps
2: 14
3: 24*
4: 10
200 kHz Max Freq @ 500 mV Peak to Peak, Freq Output
SE Channel
No. of Cycles
5:
5
Timeout (units = 0.01 seconds)
6: 1*
7: 1000
8: 0.0
Loc [ P_mb
Mult
Offset
]
;Turn off CS115
;
4: Do (P86)
1: 51*
Set Port 1* Low
5: End (P95)
6: If time is (P92)
1:
2: 60
3: 10
0
Minutes (Seconds --) into a
Interval (same units as above)
Set Output Flag High (Flag 0)
7: Real Time (P77)
1: 0110
Day,Hour/Minute (midnight = 0000)
Reps
8: Sample (P70)
1:
1
2: 1*
Loc [ P_mb
]
*Table 2 Program
02: 0.0000
Execution Interval (seconds)
*Table 3 Subroutines
End Program
-Input Locations-
1 P_mb
1 1 1
* Proper entries will vary with program and datalogger channel, and input location assignments.
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CS115 Barometric Pressure Sensor
5.1.4 Period Averaging Measurement Example for CR5000 in a Fast
Executing Program at 10Hz
EXAMPLE 4. Sample Program for CR5000
‘CR5000
'
'Sample Program to Measure CS115 Barometric Pressure Sensor
'
'
Public CS115_Freq, Pressure
Units Pressure = mb
BeginProg
Scan (100,mSec,3,0)
'Turn CS115 ON one minute before every hour
'
If (IfTime (59,60,min)) Then WriteIO (1,1)
'Period Avgeraging instruction must be executed every scan, and
'cannot be inside the "If" statement. The measured value, therefore, is
'first written into a temporary variable called "CS115_Freq".
PeriodAvg (CS115_Freq,1,mV5000,33,0,1,10,20,1.0,0)
'Once CS115 is turned on one minute before every hour, and
'the correct measurement is made, it is copied into the current variable
'called "Pressure". The sensor is, then, turned off.
'
If IfTime(0,60,min) Then
Pressure = CS115_Freq
'Turns CS115 OFF
'
WriteIO (1,0)
EndIf
NextScan
EndProg
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CS115 Barometric Pressure Sensor
5.2 Pulse Count Measurement Example
5.2.1 Pulse Count Measurement Example for 21X
EXAMPLE 5. Sample Program for 21X
;{21X}
;
*Table 1 Program
01: 1
Execution Interval (seconds)
1: If time is (P92)
1: 59
2: 60
Minutes into a
Minute Interval
Set Port 6* High
3: 46*
2: If time is (P92)
1:
2: 60
3: 30
0
Minutes into a
Minute Interval
Then Do
3: Pulse (P3)
1:
1
Reps
2: 1*
3: 24
4: 1*
Pulse Input Channel
Low Level AC, 16 Bit, Output Hz
Loc [ P_mb
Mult
]
5:
1
6: 0.0
Offset
4: Do (P86)
1: 56*
Set Port 6* Low
5: End (P95)
6: If time is (P92)
1:
0
Minutes into a
2: 60
3: 10
Minute Interval
Set Output Flag High
7: Real Time (P77)
1: 0110
Day,Hour/Minute (midnight = 0000)
8: Resolution (P78)
1:
1
High Resolution
Reps
9: Sample (P70)
1:
2:
1
1
Loc [ P_mb
]
*Table 2 Program
02: 0.0000
Execution Interval (seconds)
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CS115 Barometric Pressure Sensor
*Table 3 Subroutines
End Program
-Input Locations-
1 P_mb
1 1 1
* Proper entries will vary with program and datalogger channel, and input location assignments.
5.3 Output Resolution
When storing the values from the CS115 to a datalogger’s final storage
location, or to a data table, care must be taken to choose suitable scaling of the
reading or to store the value with adequate resolution to avoid losing useful
resolution of the pressure measurement. The default resolution (Low
Resolution) for the Campbell Scientific dataloggers is limited to a maximum of
four digits. Even then the maximum digit value that can be displayed is 6999
(7999 for the CR5000/9000 dataloggers). If you use this option with
barometric data scaled in millibars (hPa), a reading above 699.9 mb (799.9 mb
for CR5000/9000) will lose one digit of resolution, e.g. at 900mb, the
resolution is limited to 1 mb.
To retain 0.1 mb resolution, you either need to deduct a fixed offset from the
reading before it is stored to avoid exceeding the 699.9 (or 799.9) threshold, or
output the barometric reading in high resolution format. This can be done by
using the Resolution (P78) instruction in the CR500, CR510, CR10(X),
CR23X, CR7 and 21X dataloggers, or the IEEE4 format for the CR5000 and
CR9000.
6. Correcting Pressure to Sea Level
The weather service, most airports, radio stations, and television stations reduce
the atmospheric pressure to a common reference (sea level). Equation 1 can be
used to find the difference in pressure between the sea level and the site. That
value (dP) is then added to the offset (0.0 mb) in the measurement instruction.
U. S. Standard Atmosphere and dry air were assumed when Equation 1 was
derived (Wallace, J. M. and P. V. Hobbes, 1977: Atmospheric Science: An
Introductory Survey, Academic Press, pp. 59-61).
5.25328
E
dP = 1013.25 1− 1−
(1)
44307.69231
The value dP is in millibars and the site elevation, E, is in meters. Add dP
value to the offset in the measurement instruction.
Use Equation (2) to convert feet to meters.
E(ft)
E(m) =
(2)
3.281ft m
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CS115 Barometric Pressure Sensor
The corrections involved can be significant: e.g., at 1000 mb and 20°C,
barometric pressure will decrease by 1.1 mb for every 10 meter increase in
altitude.
7. Maintenance and Calibration
Since the sensor is semi-sealed, minimum maintenance is required.
1. Visually inspect the cable connection to ensure it is clean and dry.
2. Ensure that the ground connection (shield) is secure and clean.
3. Visually inspect the casing for damage.
4. Ensure that the pneumatic connection and pipe are secure and undamaged.
The external case can be cleaned with a damp, lint-free cloth and a mild
detergent solution.
Druck recommends recalibrating the CS115 every year. Contact Campbell
Scientific, Inc., phone (435) 753-2342, for an RMA number before returning
the sensor for recalibration. You may also return the unit directly to Druck
USA for recalibration.
Should you lose the five terminal connector (p/n 16004), the replacement part
can be purchased from Campbell Scientific, Inc. Contact Campbell Scientific,
Inc. to purchase the part.
The CS115 is sensitive to static when the backplate is
removed. To avoid damage, take adequate anti-static
measures when handling.
CAUTION
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Campbell Scientific Companies
Campbell Scientific, Inc. (CSI)
815 West 1800 North
Logan, Utah 84321
UNITED STATES
Campbell Scientific Africa Pty. Ltd. (CSAf)
PO Box 2450
Somerset West 7129
SOUTH AFRICA
Campbell Scientific Australia Pty. Ltd. (CSA)
PO Box 444
Thuringowa Central
QLD 4812 AUSTRALIA
Campbell Scientific do Brazil Ltda. (CSB)
Rua Luisa Crapsi Orsi, 15 Butantã
CEP: 005543-000 São Paulo SP BRAZIL
Campbell Scientific Canada Corp. (CSC)
11564 - 149th Street NW
Edmonton, Alberta T5M 1W7
CANADA
Campbell Scientific Ltd. (CSL)
Campbell Park
80 Hathern Road
Shepshed, Loughborough LE12 9GX
UNITED KINGDOM
Campbell Scientific Ltd. (France)
Miniparc du Verger - Bat. H
1, rue de Terre Neuve - Les Ulis
91967 COURTABOEUF CEDEX
FRANCE
Campbell Scientific Spain, S. L.
Psg. Font 14, local 8
08013 Barcelona
SPAIN
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