Campbell Scientific AVW1, AVW4 User Manual

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INSTRUCTION MANUAL

Use of the AVW1 and AVW4 with

Geokon Model 4500 Vibrating Wire

Piezometers and Pressure Transducers

Revision: 1/92

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.

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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

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

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

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

C (see Figure 2.2-5)

C. The precision

of the bridge resistors (±0.1%) results in a

tolerance of ±0.03

C. The accuracy of the

datalogger's voltage measurement (±0.015%)

results in a tolerance of ±0.01

C. The

temperature coefficient of the bridge resistors

(10 ppm/ ±0.0003

C) results in a tolerance of

oC/o

Errors four, five, and six mentioned above are

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

C. The temperature correction for the

±0.7 vibrating wire measurement is typically less than

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

interchangeability of ±0.5

C. The optional thermistor, Dale Electronics part number 1C3001-C3 has an inter-changeability of

C. Both of the above thermistors have the

±0.2 same resistance vs. temperature relationship as

the YSI thermistor number 44005. The following table shows the relationship

between temperature and resistance, volts, CR10 output, and linearization error.

TABLE 2.2-1. Temperature vs. Thermistor Resistance, V,

C, and Linearization Error

SENSOR

TEMP RESISTANCE, VOLTS CR10 ERROR

C OHMS OUT OUTPUT,oC

-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

C OHMS OUT OUTPUT,oC

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

C OHMS OUT OUTPUT,oC

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

AVW1/AVW4

2.3 PROGRAMMING AND SENSOR HOOK-UP

Measure the thermistor with Instruction 4 using a measurement range of 2500 mV fast, an excitation voltage of 2500 mV, a delay of 1, and a multiplier of 0.001. The resulting value is linearized with Instruction 55 using the following coefficients: C0 = -104.78, C1 = 378.11, C2 = -

611.59, C3 = 544.27, C4 = -240.91, C5 =

43.089. The output is in degrees Celsius and

covers the range from -5

C to +60oC. Due to the small current requirement, up to 118 thermistors could theoretically be powered by one excitation channel.

When measuring the Geokon temperature through CSI's AVW1 or AVW4, see Sections 4 or 5 respectively for hook up information.

NOTE: This manual covers AVW1's with serial number 1093 and up plus serial numbers 1002, 1034, 1040A, 1041, 1042, 1051, 1052, 1055, 1057, 1058, 1059, 1069, 1071, 1073, 1076, 1080, 1084, 1086, 1087, 1088, 1088A, 1089A, 1090A, 1091A, and 1092A. This manual also covers AVW4s with serial number 1045 and up plus serial numbers 1034 and 1038. These serial numbers mark a change in circuitry that changes the excitation voltage for the temperature measurement from -2500 mV (before) to +2500 mV (after). The multiplier also changed from -.001 (before) to +.001 (after). The values of the resistors in locations B4 and C4 for the AVW1 and locations D4 and E4 for the AVW4 were changed to the values shown in the current schematics.

When measuring the Geokon temperature directly with the CR10, connect the leads and bridge completion resistors as shown in Figure

2.3-1.

FIGURE 2.3-1. Direct Measurement of the

Geokon Thermistor

2-6

SECTION 3. VIBRATI NG WIRE MEASUREMENT

FIGURE 3.1-1. A Vibrating Wire Sensor

3.1 GENERAL

Figure 3.1-1 illustrates how an increase in pressure on the diaphragm decreases the tension on the wire attached to the diaphragm. A decrease in the wire tension decreases the resonant frequency in the same way that loosening a string on a guitar decreases it's frequency. Therefore, the resonant frequency of the vibrating wire sensor decreases with increasing pressure.

The Vibrating Wire Measurement Instruction excites the "plucking" and "pickup" coils shown in the above figure with a "swept" frequency. A "swept" frequency is a group of different frequencies that are sent one right after another starting with the lowest frequency and ending with the highest. The lowest and highest frequencies are entered by the user in units of hundreds of Hz. The CR10 requires 150 ms to "sweep" through all of the frequencies. This "swept" frequency causes the wire to vibrate at each of the individual frequencies. Ideally, all of the frequencies except the one matching the resonant frequency of the wire will die out in a very short time. The wire will vibrate with the resonant frequency for a relatively long period of time and as it does so it will cut the lines of flux

in the "plucking" and "pickup" coils inducing the same frequency on the lines to the CR10. After waiting for the non resonant frequencies to die out (20 ms) the CR10 accurately measures how much time it takes to receive a user specified number of cycles. Knowing the length of time and the number of cycles, the CR10 then computes the square of the frequency

expressed in units of kHz

(= 1/T2 where T is the

period in milliseconds).

3.2 MULTIPLIER & OFFSET

The 50 psi vibrating wire pressure sensor used in this example is the Geokon Model 4500SV-

50. It is vented to the atmosphere so it will not be affected by changes in barometric pressure. Each sensor is individually calibrated and has a unique set of calibration coefficients. A calibration sheet contains the Model Number, Serial Number, Gage Factor (psi/digit), Temperature Coefficient (psi/ (digits), zero Period (microseconds), calibration

Temperature (

C) and calibration Barometric Pressure (inches Hg). A Geokon "digit" is defined as the square of the frequency in kHz multiplied by 1000 (1 digit = 0.001 kHz

. The calibration coefficients for the sensor

Hz with serial number 3998 are given below:

C), Zero Reading

= 1000

3-1

AVW1/AVW4

TABLE 3.2-1. Calibration Data for Sensor 3998

Gage Factor Temp. Coeff. Zero Rdg. Period Temp. Baro.

(psi/digit) (psi/oC)

(digit) (usecond) (oC) (in Hg)

0.0151 -0.0698 9431 325.6 24 29.51

The equation to change the CR10's output into pressure (psi) exerted on the sensor is given below:

3.3 SWEPT FREQUENCY, START AND END

The AVW1 and AVW4 were not designed for

P = [M * X] + B 3.2-1 where P is the pressure in psi and X is the

result of measurement Instruction 28 in kHz

where T is the period in milliseconds). The

1/T

( =

multiplier (M) and offset (B) are determined by equations 3.2-2 and 3.2-3.

use below 1000 Hz. In general, the starting frequency of the swept

frequency for this sensor should be just a bit lower than the frequency at the Full Scale pressure of the sensor. A rough rule of thumb would put the starting frequency at two thirds that of the ending frequency. Almost always the

M = -1000(digits/kHz

) * Gage Factor 3.2-2

starting frequency should not be lower than half of the ending frequency.

where M is the multiplier in psi/(kHz Gage Factor is found on the Calibration Sheet in psi/digit.

B = Po + [Gage Factor * Zero Reading] 3.2-3 where B is the offset in psi and Po is the

pressure in psi at the time of calibration. For

) and the

Start Freq. < ([Full Scale Pressure - (Gage Factor * Zero

Reading)]/M)0.5 * 1000 Hz/kHz 3.3-1 Start Freq. < ([50psi - (0.0151psi/digit *

9431digits)]/

vibrating wire sensors not vented to the atmosphere, Po is the barometric pressure

[-15.1psi/kHz

2])0.5

* 1000 Hz/kHz ["Baro."(in Hg) * 0.49116 (psi/in Hg)] at the time of calibration. For the vented sensors, Po is 0

Start Freq. < 2474 Hz or 24 hundred Hz

psi. The Gage Factor (psi/digit) and Zero Reading (digits) are found on the Calibration Sheet.

In general, the ending frequency of the swept frequency for this sensor should be just a bit higher than the frequency at Zero Pressure.

Example: Using sensor number 3998, the multiplier, offset, and equation for pressure would be:

End Freq. > ([Zero Pressure - (Gage Factor * Zero Reading)]/M)

0.5

M = (-1000 digits/kHz M = -15.1 psi/(kHz

) * 0.0151 psi/digit

) B = 0.0 psi + (0.0151 psi/digit * 9431 digits) B = 142.4 psi P = [-15.1 psi/(kHz

) * X (kHz2)] + 142.4 psi

3-2

* 1000 Hz/kHz 3.3-2 End Freq. > ([0.0psi - (0.0151psi/digit *

9431digits)]/ [-15.1psi/kHz

2])0.5

* 1000 Hz/kHz

End Freq. > 3071 Hz or 31 hundred Hz

AVW1/AVW4

Some additional information concerning the swept frequency may be found in Appendix C.

NOTE: Please remember that sealed (or absolute) sensors calibrated near sea level will read negative at higher elevations due to the decrease in barometric pressure with increasing elevation. In most cases the solution is to load the sensor with extra external pressure to cause it to operate in its calibrated range. For example, a sealed 0 to 5 psi sensor used at 10,000 feet elevation would have to be placed under

10.6 feet of water (4.6 psi) in order to read 0 psi. This is because the barometric pressure at 10,000 feet is about 4.6 psi lower than at sea level.

3.4 RESOLUTION VS. "# OF CYCLES"

CSI and Geokon recommend that the number of cycles measured be between 200 and 500. Five hundred cycles would probably be the optimum for most applications. The measurement of more than 500 cycles is not recommended without testing. Some sensors, for example, will not vibrate a full 1000 cycles at all pressures in their pressure range.

For the sake of this discussion we will define the resolution of the vibrating wire measurement as plus or minus three standard deviations (±3 SD) of the vibrating wire measurement. The standard deviation of the measurement in psi is given by the following equation:

SD = (2*M*C)/(N*T where M is the multiplier computed in 3.2-2. "C"

is 0.00015 ms which is the typical standard deviation of a time interval measurement on the CR10 using a 4 mV peak to peak signal with no external noise. "N" is the number of cycles timed to determine the period (T) in ms of the signal being measured.

The standard deviation is greater when the period is shorter. The period is shortest at zero pressure so the "Period" at zero pressure given in Table 3.2-1 is used for the example below:

)3.4-1

SD = (2*-15.1psi/(kHz

(500 * (325.6us/1000us/ms)

) * 0.00015ms)

SD = 0.00026246 psi RESOLUTION = ±

0.00078738

psi

Resolution improves as the number of cycles measured increases but it worsens as the signal level decreases and as the noise increases. The optimum resolution is obtained when the number of cycles measured covers one time constant (τ) of the decay of the signal.

Number of cycles = (τ/T) where T is the period of the signal in

milliseconds and τ is the time in milliseconds required for the signal to decay from its initial peak to peak value to (0.368 * initial peak to peak value). An oscilloscope is required to measure the time constant. The time constants of the Geokon sensors we have measured are typically between one third second and one second.

The amount of time required to make one repetition of the vibrating wire measurement is given below:

150. ms to sweep the frequency

20. ms delay (1.5cycles + #cycles measured) * period of the

signal in ms

3.5 TEMPERATURE CORRECTION

The equation used to remove errors caused by changes in the sensor's temperature is found below:

Pt = P + (TEMP. COEFF.)*(T - To) 3.5-1 where Pt(psi) is the temperature corrected

pressure. P(psi) is the uncorrected pressure from equation 1. T( temperature of the sensor. To( "Temp." on the Calibration Sheet which is the temperature of the sensor at the time of calibration. TEMP. COEFF.(psi/ found on the Calibration Sheet. It is important to note that the "TEMP. COEFF." can be either positive or negative.

C) is the current

C) is the

C) is also

3-3

AVW1/AVW4

Example: Using sensor number 3998 and assuming a sensor temperature of 15 corrected pressure would be:

Pt = P psi + (-0.0698 psi/ = P psi + 0.6282 psi

C)*(15oC - 24oC)

3.6 DELAY BETWEEN MEASUREMENTS

The vibrating wire sensor should not be excited more often than once every five time constants if high resolution is important. If more than one repetition is specified the "delay before excitation applied" parameter can be used to ensure the proper amount of delay between excitations. Excitation of the sensor while the wire is still vibrating can cause the signals to add or subtract (in phase or out of phase) causing the wire to vibrate excessively hard or almost not at all.

C, the

If two back to back measurements are required they can be done one of two ways. With the AVW4 the repetitions parameter must be set to 2--. The "--" instructs the CR10 to excite both sensors, delay 20 ms, measure the first sensor, and then measure the second sensor. There is no delay or re-application of the excitation between the measurements. Back to back measurements require that the sum of the number of cycles measured on each sensor not exceed the time constant of the last sensor or the signal may have become too week to be measured. (e.g., two sensors measured separately, each having a time constant equal to 700 cycles would have to be measured back to back with a maximum of 350 cycles.) Back to back measurements with two AVW1s and two excitation channels can be done simply by entering Instruction 28 twice, once for the first sensor and once for the second. In this case the second AVW1 measurement will begin 170 milliseconds after the first one ended.

3-4

SECTION 4. THE AVW1

4.1 GENERAL

The AVW1 contains circuitry needed to interface Geokon's 4500 series vibrating wire sensor to the CR10. The AVW1 is designed to interface one vibrating wire sensor (temperature and pressure) to two single ended CR10 channels. The AVW1 has no quiescent current drain. The current drain during the very short (2.4 ms) temperature measurement is .4 mA or lower. The current drain during the vibrating wire measurement (170 ms to 500 ms) is 32 mA. The AVW1 is 2.5 inches long by 2.5 inches wide by 1.4 inches high. The silk screening for the AVW1 is shown below.

4.2 SENSOR HOOK UP

FIGURE 4.1-1. The AVW1

FIGURE 4.2-1. Hook up to AVW1

4.3 WELL MONITORING EXAMPLE

In this example the vibrating wire sensor is used to monitor the Distance from the lip of the well to the water surface in a 150 foot well. The water level is expected to stay within 40 to 80 feet of the lip so the 50 psi pressure sensor is placed approximately 100 feet below the lip of

the well. The same sensor used in Section 3.2 for the computation of the multiplier etc. (serial number 3998) will be used again in this example.

In the example program that follows the depth of water above the vibrating wire sensor is measured in psi and then converted into feet of

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AVW1/AVW4

water. The water depth above the sensor is referred to as the "Reading" in the following equation. The Reading decreases with increasing "Distance" from lip of well to water surface so the Distance is computed by subtracting the Reading from the Offset as shown in the above figure and the following equation.

Distance = Offset - Reading

feet (of head above the sensor). Solving the above equation for the Offset, one obtains:

Offset = Initial Distance + Initial Reading = 47.23 feet + 54.832 feet = 102.062 feet The following is a sample program that

measures the temperature and frequency of the vibrating wire sensor and stores the

temperature (

C), pressure (psi), temperature corrected pressure (psi), correction factor (psi), temperature corrected pressure (feet of H2O), and Distance from the lip to the water surface (feet) in Input Locations 1-6 respectively. This example assumes the sensor has been connected as shown in Figure 4.2-1.

Program: AVW & CR10 USED TO MEASURE 1 GEOKON VIBRATING WIRE SENSOR.

* 1 Table 1 Programs

01: 10 Sec. Execution Interval

01: P4 Excite,Delay,Volt(SE)

01: 1 Rep 02: 15 2500 mV fast Range 03: 1 IN Chan 04: 1 Excite all reps w/EXchan 1 05: 1 Delay (units .01sec) 06: 2500 mV Excitation 07: 1 Loc [:TEMP C] 08: .001 Mult 09: 0.0000 Offset

02: P55 Polynomial

01: 1 Rep 02: 1 X Loc TEMP C 03: 1 F(X) Loc [:TEMP C] 04: -104.78 C0 05: 378.11 C1 06: -611.59 C2 07: 544.27 C3 08: -240.91 C4 09: 43.089 C5

FIGURE 4.3-1. Well Monitoring Example

The "Initial Distance" to the water surface is measured with a chalked line to be 47.23 feet below the lip. The "Initial Reading" is 54.832

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AVW1/AVW4

03: P28 Vibrating Wire (SE)

01: 1 Rep 02: 2 IN Chan 03: 1 Excite all reps w/EXchan 1 04: 24 Starting Freq. (units=100 Hz) 05: 31 End Freq. (units=100 Hz) 06: 500 No. of Cycles 07: 0000 Rep delay (units=.01sec) 08: 2 Loc [:PRESS psi] 09: -15.1 Mult 10: 142.4 Offset

04: P34 Z=X+F

01: 1 X Loc TEMP C 02: -24 F calibration "Temp." in C 03: 4 Z Loc [:(T-To)*C]

05: P37 Z=X*F

01: 4 X Loc (T-To)*C 02: -.0698 F "Temp. Coeff." 03: 4 Z Loc [:(T-To)*C]

06: P33 Z=X+Y

01: 2 X Loc PRESS psi 02: 4 Y Loc (T-To)*C] 03: 3 Z Loc [:Pt psi]

07: P37 Z=X*F Converts psi to

negative ft H20 01: 3 X Loc Pt psi 02: -2.3067 F 03: 5 Z Loc [:-Pt FEET H20]

08: P34 Z=X+F Adds the Offset to the

negative of the Reading to

obtain the Distance from lip of

the well to water surface. 01: 5 X Loc -Pt FEET H20 02: 102.06 F OFFSET 03: 6 Z Loc [:DISTANCE FEET]

09: P End Table 1

First 99 Input Location Labels: 1:TEMP C 2:PRESS psi 3:Pt psi 4:(T-To)*C 5:Pt Ft H20 6:DISTAN FT

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AVW1/AVW4

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SECTION 5. THE AVW4

5.1 GENERAL

The AVW4 contains circuitry needed to interface Geokon's 4500 series vibrating wire sensor to the CR10. The AVW4 is designed to interface four vibrating wire sensors (temperature and pressure) to eight single ended CR10 channels. The AVW4 has no

quiescent current drain. The current drain during the very short (2.4 ms) temperature measurement is .4 mA per channel or lower. The current drain during each vibrating wire measurement (170 ms to 500 ms) is 32 mA. The AVW4 is 6.7 inches long by 2.9 inches wide by 1.4 inches high.

FIGURE 5.1-1. The AVW4

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AVW1/AVW4

5.2 SENSOR HOOK UP

FIGURE 5.2-1. Hook up for AVW4

5.3 DATALOGGER PROGRAMMING

The following is a sample program that measures four sealed Geokon sensors and stores the temperature, pressure, pressure corrected for temperature, and barometric corrected pressure in psi in Input Locations 1..4,

5..8, 9..12, and 10..12 respectively. The example utilizes the calibration data given previously from sensor number 3998. The first sensor measures barometric pressure only and is used to remove atmospheric pressure changes from the readings on the other three sensors. This example assumes the sensors have been connected as shown in the sensor hookup diagram.

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Program: AVW4 & CR10 USED TO MEASURE 4 GEOKON SENSORS. THE FIRST SENSOR SERVES AS A BAROMETER AND IS SUBTRACTED FROM THE OTHER THREE TO MEASURE THREE WATER PRESSURES IN PSI EVERY FIVE MINUTES.

* 1 Table 1 Programs

01: 300 Sec. Execution Interval

01: P4 Excite,Delay,Volt(SE)

01: 4 Reps 02: 15 2500 mV fast Range 03: 1 IN Chan 04: 1 Excite all reps w/EXchan 1 05: 1 Delay (units .01sec) 06: 2500 mV Excitation 07: 1 Loc [:TEMP C #1] 08: .001 Mult 09: 0.0000 Offset

AVW1/AVW4

02: P55 Polynomial

01: 4 Reps 02: 1 X Loc TEMP C #1 03: 1 F(X) Loc [:TEMP C #1] 04: -104.78 C0 05: 378.11 C1 06: -611.59 C2 07: 544.27 C3 08: -240.91 C4 09: 43.089 C5

03: P28 Vibrating Wire (SE)

01: 4 Reps 02: 5 IN Chan 03: 1 Excite all reps w/EXchan 1 04: 24 Starting Freq. (units=100 Hz) 05: 31 End Freq. (units=100 Hz) 06: 500 No. of Cycles 07: 500 Rep delay (units=.01sec) 5

SEC DELAY BETWEEN

MEASUREMENTS 08: 5 Loc [:P psi #1] 09: 1 Mult 10: 0 Offset

04: P53 Scaling Array (A*loc +B)

APPLY MULT & OFFSET 01: 5 Start Loc [:P psi #1] 02: -15.1 A1 03: 142.4 B1 04: -15.1 A2 05: 142.4 B2 06: -15.1 A3 07: 142.4 B3 08: -15.1 A4 09: 142.4 B4

07: P34 Z=X+F ASSUMES

CALIBRATION TEMP. = 24 01: 1-- X Loc TEMP C #1 02: -24 F 03: 17-- Z Loc [:T-To*C #1]

08: P36 Z=X*Y

01: 13-- X Loc Cpsi/C #1 02: 17-- Y Loc T-To*C #1 03: 17-- Z Loc [:T-To*C #1]

09: P33 Z=X+Y

01: 5-- X Loc psi #1 02: 17-- Y Loc T-To*C #1 03: 9-- Z Loc [:Pt psi #1]

10: P95 End FOLLOWING THREE INSTRUCTIONS

SUBTRACT THE BAROMETRIC PRESSURE FROM THE THREE WATER PRESSURES

11: P35 Z=X-Y

01: 10 X Loc Ptb psi #2 02: 9 Y Loc Pt psi #1 03: 10 Z Loc [:Ptb psi #2]

12: P35 Z=X-Y

01: 11 X Loc Ptb psi #3 02: 9 Y Loc Pt psi #1 03: 11 Z Loc [:Ptb psi #3]

13: P35 Z=X-Y

01: 12 X Loc Ptb psi #4 02: 9 Y Loc Pt psi #1 03: 12 Z Loc [:Ptb psi #4]

05: P53 Scaling Array (A*loc +B)

LOADS TEMP. COEFF. 01: 13 Start Loc [:Cpsi/C #1] 02: 0 A1 03: -.0698 B1 04: 0 A2 05: -.0698 B2 06: 0 A3 07: -.0698 B3 08: 0 A4 09: -.0698 B4

06: P87 Beginning of Loop

TEMPERATURE

CORRECTION 01: 00 Delay 02: 4 Loop Count

First 99 Input Location Labels: 1:TEMP C #1 11:Ptbpsi #3

2:TEMP C #2 12:Ptbpsi #4 3:TEMP C #3 13:Cpsi/C #1 4:TEMP C #4 14:Cpsi/C #2 5:P psi #1 15:Cpsi/C #3 6:P psi #2 16:Cpsi/C #4 7:P psi #3 17:T-To*C #1 8:P psi #4 18:T-To*C #2 9:Pt psi #1 19:T-To*C #3 10:Ptbpsi #2 20:T-To*C #42

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AVW1/AVW4

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APPENDIX A. PRESSURE CONVERSION CHART

A-1

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APPENDIX B. SCHEMATICS AND STUFFING CHARTS FOR

AVW1 AND AVW4

B-1