Campbell Scientific AVW1, AVW4 User Manual
INSTRUCTION MANUAL
Use of the AVW1 and AVW4 with
Geokon Model 4500 Vibrating Wire
Piezometers and Pressure Transducers
Revision: 1/92
Copyright (c) 1987-1992
Campbell Scientific, Inc.
Warranty and Assistance
The AVW1 AND AVW4 are warranted by CAMPBELL SCIENTIFIC, INC.
to be free from defects in materials and workmanship under normal use and
service for twelve (12) months from date of shipment unless spec ified
otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC, INC.'s
obligation under this warranty is limited to repairing or replacing (at
CAMPBELL SCIENTIFIC, INC.'s option) defective products. The customer
shall assume all costs of removing, reinstalling, and shipping defective products
to CAMPBELL SCIENTIFIC, INC. CAMPBELL SCIENTIFIC, INC. will
return such products by surface carrier prepaid. This warranty shall not apply
to any CAMPBELL SCIENTIFIC, INC. products which have been subjected to
modification, misuse, neglect, accidents of nature, or shipping damage. This
warranty is in lieu of all other warranties, expressed or implied, including
warranties of merchantability or fitness for a particular purpose. CAMPBELL
SCIENTIFIC, INC. is not liable for special, indirect, incidental, or
consequential damages.
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 custome rs within their territorie s. P lease visit www.ca m pbells ci.com to
determine which Campbell Scientific company serves your country. To obtain
a Returned Materials Authorization (RMA), contact CAMPBELL
SCIENTIFIC, INC., phone (435) 753-2342. 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
CAMPBELL SCIENTIFIC, INC. does not accept collect calls.
TABLE OF CONTENTS
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PAGE
WARRANTY AND ASSISTANCE
1. GENERAL INFORMATION
1.1 Sensor Selection ..............................................................................................................................1-1
1.2 Sensor Care and Installation.............................................................................................. ..............1-1
2. TEMPERATURE MEASUREMENT
2.1 General.............................................................................................................................................2-1
2.2 Accuracy and Resolution..................................................................................................................2-1
2.3 Programming and Sensor Hook-up..................................................................................................2-6
3. VIBRATING WIRE MEASUREMENT
3.1 General.............................................................................................................................................3-1
3.2 Multiplier and Offset..........................................................................................................................3-1
3.3 Swept Frequency, Start and End......................................................................................................3-2
3.4 Resolution vs. "# of cycles" ..............................................................................................................3-3
3.5 Temperature Correction ...................................................................................................................3-3
3.6 Delay Between Measurements.........................................................................................................3-4
4. THE AVW1
4.1 General.............................................................................................................................................4-1
4.2 Sensor Hook Up...............................................................................................................................4-1
4.3 Well Monitoring Example..................................................................................................................4-1
5. THE AVW4
5.1 General.............................................................................................................................................5-1
5.2 Sensor Hook Up...............................................................................................................................5-2
5.3 Datalogger Programming .................................................................................................................5-2
6. THE AVW1 AND A MULTIPLEXER
Not yet available
APPENDIX A. PRESSURE CONVERSION CHART............................................... A-1
APPENDIX B. SCHEMATICS AND STUFFING CHARTS ......................................B-1
APPENDIX C. THEORY AND ADDITIONAL DETAILS
C.1 Swept Frequency Theory................................................................................................................C-1
C.2 Additional Theory on Multiplier and Offset......................................................................................C-1
I
TABLE OF CONTENTS
TABLES
2.2-1 Temperature vs. Thermistor Resistance, V, oC, and Linearization Error................................... 2-1
3.2-1 Calibration Data for Sensor 3998................................................................................................ 3-2
FIGURES
2.2-1 Temperature Measurement Error at Three Temperatures as a Function of Lead Length ......... 2-3
2.2-2 Temperature Measurement Error on a 1000 Foot Lead............................................................. 2-4
2.2-3 Temperature Measurement Error on a 3000 Foot Lead............................................................. 2-4
2.2-4 Temperature Measurement Error on a 5000 Foot Lead............................................................. 2-5
2.2-5 Thermistor Linearization Error .................................................................................................... 2-5
2.3-1 Direct Measurement of the Geokon Thermistor.......................................................................... 2-6
3.1-1 A Vibrating Wire Sensor.............................................................................................................. 3-1
4.1-1 The AVW1................................................................................................................................... 4-1
4.2-1 Hook up to AVW1 ....................................................................................................................... 4-1
4.3-1 Well Monitoring Example............................................................................................................ 4-2
5.1-1 The AVW4................................................................................................................................... 5-1
5.2-1 Hook up for AVW4...................................................................................................................... 5-2
A.1 Pressure Conversion Chart.........................................................................................................A-1
B.1-1 AVW1 Schematic........................................................................................................................B-1
B.1-2 AVW1 Stuffing Chart...................................................................................................................B-2
B.1-3 AVW4 Schematic........................................................................................................................B-3
B.1-4 AVW4 Schematic........................................................................................................................B-4
B.1-5 AVW4 Stuffing Chart...................................................................................................................B-5
II
USE OF THE AVW1 AND AVW4 WITH GEOKON MODEL 4500
VIBRATING WIRE PI EZOMETERS AND PRESSURE TRANSDUCERS
1. GENERAL INFORMATION
The CR10 is the only CSI datalogger that has
the capability of measuring the vibrating wire
pressure sensor in addition to the piezoresistive
type of strain gage sensor. The CR10 can
measure vibrating wire sensors with short leads
without the AVW1 or AVW4. However, the
AVW1 and AVW4 provide important signal
conditioning that 1) completes the thermistor
bridge for the measurement of the sensor's
temperature, 2) converts the swept frequency
excitation from 2.5 volts peak to peak to 12
volts peak to peak, 3) provides transformer
isolation and consequent noise reduction for the
vibrating wire signal, and 4) provides additional
transient protection for both the temperature
and vibrating wire circuits.
The AVW1 and AVW4 are designed and tested
over the environmental range from -25°C to
+50°C. CSI recommends that special
temperature testing be done at the factory if the
AVW's are to operate at temperatures outside
this range.
1.1 SENSOR SELECTION
The vibrating wire sensors may be purchased
as either vented or sealed sensors. The vented
sensors have a small hollow "vent tube" that
connects the hollow chamber behind the
diaphragm to the atmosphere. The vent tube
allows the barometric pressure to act on both
sides of the diaphragm equally which removes
the barometric pressure from the reading. A
pressure reading with out a barometric pressure
component is referred to as "gage" pressure. A
pressure reading with a barometric pressure
component is referred to as "absolute"
pressure. One disadvantage of the vented
sensor is that the cable, which contains the vent
tube, is more expensive than the cable for the
unvented sensor. For this reason, it may be
more economical to buy unvented sensors and
use an extra one as a barometer to remove the
barometric pressure. A second small
disadvantage of the vented sensors is that they
require the use of desiccant, which must be
changed periodically, to dry the air entering the
vent tube.
The vibrating wire pressure sensor has a good
reputation for long term stability. The sensor
utilizes a change in the frequency of a vibrating
wire to sense pressure. Two measurements
are usually made on a vibrating wire sensor.
The first is the measurement of the temperature
of the probe to compensate for changes in its
temperature. The second is the measurement
of the frequency of the vibrating wire.
This manual covers the use of the CR10 and
AVW1 or AVW4 with Geokon's Model 4500
vibrating wire sensor series. Sections 2 and 3
of this manual cover the temperature and
vibrating wire measurements respectively.
Sections 4 and 5 give detail concerning the use
of the AVW1 and AVW4.
Geokon includes a calibration sheet and
instruction manual with each sensor or group of
sensors they sell. Geokon's manual should be
consulted for information on sensor selection
and installation. Geokon's address and phone
number are: 48 Spencer Street, Lebanon, NH
03766, (603) 448-1562.
1.2 SENSOR CARE AND INSTALLATION
The moisture trap of the vented models should
be kept closed until readings are to be taken.
DO NOT FORGET to remove the screw that
plugs the moisture trap when readings are to be
taken.
The large diameter diaphragm used in the low
pressure sensor requires special care when
handling. Avoid bumping or jarring the sensor.
Orientation of the 4500 series sensors will affect
the zero reading. Readings should be taken
with the sensor in the same orientation at all
times. When installing the 4500 series sensors,
certain steps should be followed to obtain
proper zero readings.
The cavity between the sintered filter cap and
the diaphragm should be filled with clean water
without any air bubbles.
In most cases the sensor is made to output
water height or pressure relative to a measured
level. In this case the pressure sensor should
1-1
AVW1/AVW4
be placed at the desired level and allowed to
come to temperature equilibrium with its
surroundings (5 minutes or more). The
multiplier determined in equation 3.2-2 should
be entered and 0.0 should be entered for the
offset. After the temperature and the reading
has stabilized, determine the value that would
have to be added to the reading to obtain the
measured level. Enter this value as the offset.
In some cases there is no measured reference.
In order to obtain the correct offset under these
conditions, lower the sensor to a point just
above the water level and wait 5 minutes. Use
the multiplier, an offset of 0.0, and the
temperature correction function determined in
Sections 3.2 and 3.5 to obtain a reading.
Record the reading. Solve equation 3.2-3 for
the new offset by plugging in the "reading" in the
place of the "[Gage Factor * Zero Reading]" and
the "Barometric Pressure" from an accurate
barometer or a reference sensor in the place of
"Po" unless it is a vented sensor then use 0 in
the place of "Po". Enter the new offset.
1-2
SECTION 2. TEMPERATURE MEASUREMENT
2.1 GENERAL
The vibrating wire probe includes a thermistor
which is used to measure the temperature of
the probe. Probe temperature is used to correct
errors in the vibrating wire measurement
caused by changes in the temperature of the
probe. The temperature correction is most
important when the temperature of the medium
the probe is measuring is changing (e.g. water
temperature in a river or shallow lake). When
concerned with the absolute reading, it is also
important to make the temperature correction if
the medium temperature differs from the
calibration temperature. In a deep well where
the water temperature does not change, the
error due to temperature can be removed by
allowing the sensor to come to thermal
equilibrium and adjusting the sensor reading to
read the correct depth by means of an offset.
2.2 ACCURACY AND RESOLUTION
The accuracy of the temperature measurement
is a function of the following factors listed in
decreasing importance: 1) the thermistor's
interchangeability, 2) the resistance of the wire,
3) the linearization error, 4) the precision of the
bridge resistors, 5) the accuracy of the
datalogger's voltage measurement, and 6) the
temperature coefficient of the bridge resistors.
The interchangeability of the thermistor is
o
C although a thermistor with ±0.2oC
±0.5
interchangeability is an option. The error due to
wire resistance is normally less than ±0.5
(see Figure 2.2-1 through 2.2-4). The
linearization error is ±0.15
over the range from -5 to +60
ο
C (see Figure 2.2-5)
o
C. The precision
of the bridge resistors (±0.1%) results in a
o
tolerance of ±0.03
C. The accuracy of the
datalogger's voltage measurement (±0.015%)
o
results in a tolerance of ±0.01
C. The
temperature coefficient of the bridge resistors
o
(10 ppm/
±0.0003
C) results in a tolerance of
oC/o
C.
Errors four, five, and six mentioned above are
o
all less than ±0.03
C each and can probably be
ignored. The wire resistance is primarily an
offset error and its affect on the pressure
measurement is removed by the initial
calibration. Errors caused by the change in wire
resistance due to temperature, thermistor
interchangeability, and the linearization error are
not removed by the initial calibration.
Ignoring the offset errors, the remaining
temperature accuracy is expected to be about
o
C. The temperature correction for the
±0.7
vibrating wire measurement is typically less than
o
0.05 psi/
C. A ±0.7oC temperature error would
result in a 0.035 psi (±1.0 inch H2O) error on a
50 psi Full Scale range.
The thermistor, Dale Electronics part number
1C3001-B3 is the standard with an
o
interchangeability of ±0.5
C. The optional
thermistor, Dale Electronics part number
1C3001-C3 has an inter-changeability of
o
C. Both of the above thermistors have the
±0.2
same resistance vs. temperature relationship as
o
C
the YSI thermistor number 44005.
The following table shows the relationship
between temperature and resistance, volts,
CR10 output, and linearization error.
o
TABLE 2.2-1. Temperature vs. Thermistor Resistance, V,
C, and Linearization Error
SENSOR
TEMP RESISTANCE, VOLTS CR10 ERROR
o
C OHMS OUT OUTPUT,oC
o
C
-5 12700 0.668449 -5.09136 -0.09136
-4 12050 0.692520 -4.02248 -0.02248
-3 11440 0.716743 -2.98315 0.016846
-2 10860 0.741399 -1.95557 0.044427
-1 10310 0.766400 -0.93843 0.061560
2-1
AVW1/AVW4
SENSOR
TEMP RESISTANCE, VOLTS CR10 ERROR
o
C OHMS OUT OUTPUT,oC
o
C
0 9796 0.791339 0.057084 0.057084
1 9310 0.816459 1.045822 0.045822
2 8851 0.841694 2.029469 0.029469
3 8417 0.867031 3.011520 0.011520
4 8006 0.892474 3.995450 -0.00454
5 7618 0.917902 4.979594 -0.02040
6 7252 0.943253 5.963992 -0.03600
7 6905 0.968616 6.954119 -0.04588
8 6576 0.993956 7.950259 -0.04974
9 6265 1.019160 8.949209 -0.05079
10 5971 1.044190 9.950388 -0.04961
11 5692 1.069107 10.95688 -0.04311
12 5427 1.093900 11.96879 -0.03120
13 5177 1.118368 12.97814 -0.02185
14 4939 1.142700 13.99297 -0.00702
15 4714 1.166697 15.00510 0.005100
16 4500 1.190476 16.01954 0.019545
17 4297 1.213945 17.03265 0.032652
18 4105 1.237011 18.04042 0.040421
19 3922 1.259826 19.04982 0.049822
20 3748 1.282314 20.05785 0.057855
21 3583 1.304393 21.06127 0.061275
22 3426 1.326119 22.06310 0.063105
23 3277 1.347418 23.06048 0.060484
24 3135 1.368363 24.05747 0.057474
25 3000 1.388888 25.05167 0.051679
26 287 1.408926 26.04042 0.040428
27 2750 1.428571 27.02901 0.029014
28 2633 1.447932 28.02396 0.023968
29 2523 1.466619 29.00577 0.005777
30 2417 1.485089 29.99901 -0.00098
31 2317 1.502945 30.98300 -0.01699
32 2221 1.520496 31.97513 -0.02486
33 2130 1.537515 32.96311 -0.03688
34 2042 1.554339 33.96711 -0.03288
35 1959 1.570549 34.96239 -0.03760
36 1880 1.586294 35.95767 -0.04232
37 1805 1.601537 36.95011 -0.04988
38 1733 1.616448 37.95060 -0.04939
39 1664 1.631002 38.95742 -0.04257
40 1598 1.645169 39.96844 -0.03155
41 1535 1.658925 40.98115 -0.01884
42 1475 1.672240 41.99263 -0.00736
43 1418 1.685090 42.99951 -0.00048
44 1363 1.697677 44.01695 0.016954
45 1310 1.709986 45.04335 0.043350
46 1260 1.721763 46.05610 0.056109
47 1212 1.733222 47.07191 0.071918
48 1167 1.744104 48.06568 0.065681
2-2
AVW1/AVW4
SENSOR
TEMP RESISTANCE, VOLTS CR10 ERROR
o
C OHMS OUT OUTPUT,oC
o
C
49 1123 1.754878 49.07873 0.078734
50 1081 1.765287 50.08636 0.086361
51 1040 1.775568 51.11067 0.110677
52 1002 1.785204 52.09809 0.098095
53 965 1.794687 53.09674 0.096746
54 929.6 1.803855 54.08849 0.088499
55 895.8 1.812697 55.07032 0.070322
56 863.3 1.821281 56.04819 0.048193
57 832.2 1.829571 57.01651 0.016519
58 802.3 1.837613 57.97896 -0.02103
59 773.7 1.845372 58.92977 -0.07022
60 746.3 1.852867 59.86962 -0.13037
FIGURE 2.2-1. Temperature Measurement Error at Three Temperatures as a Function of Lead
Length. Wire is 22 AWG with 16 ohms per 1000 feet.
2-3
AVW1/AVW4
FIGURE 2.2-2. Temperature Measurement Error on a 1000 foot Lead. Wire is 22 AWG with 16
ohms per 1000 feet.
FIGURE 2.2-3. Temperature Measurement Error on a 3000 foot Lead. Wire is 22 AWG with 16
ohms per 1000 feet.
2-4
AVW1/AVW4
FIGURE 2.2-4. Temperature Measurement Error on a 5000 foot Lead. Wire is 22 AWG with 16
ohms per 1000 feet.
FIGURE 2.2-5. Thermistor Linearization Error
2-5
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