Evaluation of Equipment for 

Measurement of Water Level 

D in Wells of Small Diameter

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il

GEOLOGICAL SURVEY 

CIRCULAR 453

Evaluation of Equipment for 

Measurement of Water Level 

in Wells of Small Diameter

By Eugene Shuter and A. I. Johnson

GEOLOGICAL SURVEY. CIRCULAR 453

Washington 

T96T
United States Department of the Interior

STEWART L. UDALL, SECRETARY

Geological Survey

THOMAS B. NOLAN, DIRECTOR

Free on application'to the U.S. Geological Survey, Washington 25, D. C.
CONTENTS

Page

Abstract _____________________________ 1

Introduction __________________________ 1

Purpose and scope__________________ l

History.___________________________ 2

Organization ______________________ 2

Acknowledgments _ __________________ 2

Methods of investigation_______________ 3

Techniques ________________________ 3

Laboratory phase _________________ 3

Field phase ______________________ 3

Description and operation of

equipment ______________________ 4

Drescher float-gage attachment ____ 4

Columbus cradle-gage attachment __ 5

Koopman ferret-gage attachment ___ 6

Other water-level equipment _______ 7

Page 

Evaluation of equipment_______________ 8

Drescher, Columbus, and Koopman

attachments ____________________ 8

Recording accuracy ______________ 8

Rate of response to water-level

movement ____________________ 10.

Ease of repair in field ____________ 10

Stability under influence of

weather ______________________ 10

Ease of installation_______________ 10

Adaptability to standard w.aterlevel recorders _______________ 11

Other equipment ___________________ 11

Summary. ___________________________ 11

References __________________________ 12

ILLUSTRATIONS

Page 

Figure 1. A standard-type water-level recorder______________________________________ 1

2. Laboratory tank for testing gage attachments _______________________________ 3

3. Floats used in testing gage attachments______________ _____________________ 3

4. Drescher float-gage attachment _______________ __________________________ 4

5.. Columbus cradle-gage attachment _________________________________________ 5

6. Koopman ferret-gage attachment ______________ __________________________ 6

7. Comparison of water-level record from recorder with 3^-inch-diameter 

float with record from similar recorder with Drescher float-gage 

attachment and 1?-inch-diameter plastic float__ ____________________ __ 8

8. Drescher float-gage record showing the effect of float and float-line "drag"_____ 9

9. Columbus cradle-gage record showing the effect of float and float-line "drag" __ 9

10. Comparison of water-level record from recorder with 3^-inch-diameter float

with record from similar recorder with Koopman ferret-gage attachment ___ 9

11. Effects of weak batteries on water-level records obtained by use of recorder 

equipped with the Drescher float-gage attachment, the Columbus cradlegage attachment, and conventional 3y-inch-diameter float _________________ 10

III

Evaluation of Equipment for Measurement of 

Water level in Wells of Small Diameter

By Eugene Shuter and A. I. Johnson

ABSTRACT

For many years hydrologists have needed a device for 

recording the changes of water level in wells less thgm 4 inches in diameter. The hydrologic laboratory, U.S. Geological 

Survey, Denver, Colo., was assigned the responsibility of 

evaluating several models of such devices that have been 

developed in recent years. The assignment included laboratory and field evaluation of three major units the Drescher 

float-gage, Columbus era die-gage, and the Koopman ferretgage attachments all developed by personnel of the Geological Survey. Several other devices were evaluated by 

examination or by study of pertinent literature and plans.

The evaluation indicated that none of the units meets all 

field requirements. The Koopman ferret-gage attachment was 

found to be the most versatile, reliable, and accurate of those 

evaluated. The Drescher float-gage attachment is recommended 

for use on wells having a shallow depth to water. The evaluation indicated also that electronic pressure transducers might 

be potentially useful for water-level measurement.

INTRODUCTION

PURPOSE AND SCOPE

In 1937, Q. E. Meinzer, chief of the Ground 

Water Branch of the U.S. Geological Survey, 

stated, "The automatic water-stage recorders 

are among the most valuable instruments of 

precision used in the study of ground water." 

In all types of water-resources investigations 

throughout the world the water-stage recorder 

(also called water-level recorder or recording gage) has become an important instrument 

for obtaining continous records of water-level 

fluctuations in wells.

Nearly all water-level recorders now used 

are of the mechanical, float-actuated type. 

(See fig. 1.) The recording energy is produced 

by the movement of afloat as it rises or falls 

with changes in water level. The float is fastened to a flexible cable that extends upward, 

over a pulley, and downward to a counterweight at the other end. The pulley is connected to a recording drum that revolves as 

the cable moves, and a trace of the waterlevel fluctuations is made by a clock-actuated 

pen that moves across the chart.

A certain minimum force is required to 

move the mechanism of the recorder. This 

actuating force must be supplied from the 

float and must be sufficient to overcome 

mechanical losses due to the bending of the 

cable over the pulley, gear play, friction in 

the bearings and gears, and friction of the 

pen on the paper. Stevens [no date, p. 20] 

suggests that the float lag (lag of the record 

behind the true water level) is directly proportional to the force required to move the 

mechanism and is inversely proportional to

B

Figure 1. A standard-type water-level recorder. A, Side view; 

£j Front view.
EVALUATION OF EQUIPMENT FOR MEASUREMENT OF WATER LEVEL IN WELLS OF SMALL DIAMETER

the square of the float diameter. The force 

available for sufficient response energy to 

operate a recording gage is equal to the 

weight of water corresponding to the fraction 

of the volume of the float emerged or submerged as a result of change in water level. 

Small-diameter floats have a lesser amount 

of usable force; consequently, this force must 

be magnified by a mechanical attachment to 

obtain adequate recording ability.

A float of sufficient size to produce an acceptable record can only be used in a well 

having a minimum diameter of 4 inches. Because of the expense of constructing wells 4 

inches or more in diameter and because of 

the need for obtaining records of water levels 

by means of a float lowered into the narrow 

annular space around the pump column in a 

pumped well, a device to record these water 

levels accurately has been greatly needed.

During the past few years several gage attachments or mechanisms for use in recording water-level changes in small-diameter 

wells have been proposed and constructed. 

The purpose of this project was to test and 

evaluate some qf these units.

Three units the Drescher float-gage attachment, the Columbus cradle-gage attachment, and the Koopman ferret-gage attachment were evaluated. Several1 other devices 

were evaluated by examination and by study 

of pertinent plans, literature, correspondence, 

and, in some cases, the equipment itself. The 

evaluation in the laboratory -and field was 

limited to equipment for which at least one 

pilot model had been constructed previously 

and which showed the most promise at the 

time the project was begun. The lack of duplicate pilot models of the three units evaluated in this report prevented simultaneous 

evaluation at different field locations.

HISTORY

Many substitutes for the standard recorder 

float have been used in attempts to record 

water levels in small-diameter wells. During 

the past 10 years, these substitutes have become more elaborate and many have taken 

the form of electrically actuated, motor - 

powered devices designed to overcome the 

float lag caused by small-diameter floats.

In 1947, W.G. Keck, consulting geophysicist, 

East Lansing, Mich., designed the "Keck immersion element" one of the first known 

workable models of an electrically activated 

float.

In 1954, J. H. Criner, engineer of the 

Ground Water Branch,- Memphis, Term., developed the "Criner gage attachment."

In 1955, W. J. Drescher,branch area chief, 

Ground Water Branch, U.S. Geological Survey, 

Madison, Wis., developed the "Drescher floatgage attachment."

In 1956, F. C. Koopman, engineer of the 

hydrologic laboratory, U.S. Geological Survey, Denver, Colo., developed the "Koopman 

ferret-gage attachment."

In 1959, the equipment-development laboratory, U.S. Geological Survey, Columbus, 

Ohio, developed the "Columbus cradle-gage 

attachment."

ORGANIZATION

Recognizing the great need for the evaluation of equipment to measure water levels in 

small-diameter wells, the junior author for-' 

mally proposed the evaluation project in the 

spring of 1958 and started the preliminary 

investigation. The senior author was designated project leader in July 1959, and the 

project was continued by him under the general supervision of the junior author, who is 

chief of the hydrologic laboratory. The project was carried out at the laboratory in 

Denver, Colo. Some studies were made also 

at offices of the Ground Water Branch in 

several States.

ACKNOWLEDGMENTS

Field-evaluation data were provided by 

Messrs. W. J. Drescher and C. L. R. Holt of 

the Madison, Wis., off ice of the Ground Water 

Branch and by V. C. Fishel and S. W. Fader 

of the Lawrence, Kans., office. Many others 

of the Branch made helpful suggestions regarding the operation of this equipment.
METHODS OF INVESTIGATION

METHODS OF INVESTIGATION

TECHNIQUES

A

LABORATORY PHASE

Three units the Drescher float-gage attachment, the Columbus cradle-gage attachment, and the Koopman ferret-gage attachment were tested under variable temperature and humidity conditions in a temporary 

outdoor laboratory and under controlled temperature and humidity conditions in the main 

laboratory. In both locations, the three units 

were tested simultaneously in a tank (fig. 2) 

in which the water level could be made to 

fluctuate in any desired cycle. The gage attachments were actuated by small-diameter 

floats suspended within 2-inch inside diameter plastic-tube "wells" in the test tank. All 

units were tested on Stevens type-F recorders (fig. 1), but the attachments were designed to function with any type of float gage 

using a pulley on a horizontal shaft to drive 

the recording mechanism. A Stevens type-F 

water-level recorder equipped with a 3|- 

inch-diameter float provided a standard for 

comparison with the three tested gage attachments.

Several different switches, relays, motor 

drives, and other parts of the gage attachments were investigated to obtain components 

giving maximum efficiency and economy.

SJ/2-lnch

Float line ta 

standard recorder

\|

'" >- !' «' " > (,! '« 1.*

p

?£^l

m

Figure 2. Laboratory tank for testing gage attachments.

Figure 3. Floats used in testing gage attachments. Floats A D 

and F H are plastic; float E is cork with lead ballast.

Eight floats of different design were tested in 

order to obtain the best possible float and 

gage combinations. (See fig. 3.) Only those 

floats found to be the most satisfactory are 

discussed in the remainder of the report.

FIELD PHASE

All three gage attachments were tested in 

the field; however, this testing was less comprehensive than that in the laboratory.

The Columbus cradle-gage attachment was 

tested extensively in Wisconsin. The attachment was equipped with a float, 1 inch in
EVALUATION OF EQUIPMENT FOR MEASUREMENT OF WATER LEVEL IN WELLS OF SMALL DIAMETER

diameter and 11 inches long (float B t fig. 3)^ 

which in turn was installed in l^-inch steel 

pipe (1.38-inch inside diameter) suspended 

within a 6-inch-diameter well. A 3^-inchdiameter float attached to a standard waterlevel recorder was installed in the space between the li-inch pipe and the wall of the 6- 

inch-diameter well. Thus, the water-level 

changes were recorded simultaneously on 

both recorders. The average depth to water 

was 72 feet. The maximum change in water 

level was approximately 1 foot.

The Drescher float-gage attachment was 

tested in several observation wells in Wisconsin, Colorado, and Kansas. In Wisconsin 

the gage attachment, equipped with a float 1 

inch in diameter and 12 inches long (float A , 

fig. 3), was installed on shallow wells constructed of l^-inch steel pipe. In Kansas the 

gage attachment was installed in li-inchpipe wells having a depth to water of approximately 150 feet. In Colorado the gage attachment, equipped with a 1^ -inch -diameter float 

(float H , fig. 3), was installed in a 2-inch 

plastic pipe. The 2-inch oipe was suspended 

in lan 8-inch-diameter well. Daily waterlevel measurements were made by steel tape 

for control. The average depth to water was 

263 feet.

The Koopman ferret-gage attachment was 

tested in the hydrologic laboratory's observation well at Denver, Colo. It was equipped 

with a 1-inch detector probe and was installed 

in a 3-inch plastic pipe. Daily water-level 

measurements were made by tape for control. 

The average distance from the recorder to 

the water surface was 10 feet.

DESCRIPTION AND OPERATION OF EQUIPMENT

DRESCHER FLOAT-GAGE ATTACHMENT

The Drescher .float-gage attachment is 

added to the standard recorder to record water levels in small-diameter wells (fig. 4). 

The device is unique in its design and in the 

assembly of the parts but not in the parts 

themselves. The unit uses a small-diameter 

float connected to a float line, which runs 

from the float over a pulley on the end of a 

balance arm, and thence around the recorder 

pulley to a motor-driven reel powered by two 

6-volt lantern batteries in series. A float 

movement causes the balance arm and attached mercury switch to tilt, and the resulting electrical contact starts the motor,

Figure 4. Drescher float-gage attachment. A. Side view; fl, 

Front view.

causing the float-line reel to retrieve or release cable until the balance arm returns to 

the equilibrium position. This movement of 

cable on or off the reel turns the drum of the 

recorder. AnL-shaped stand which holds the 

balance arm, motor, and reel assembly, is a 

convenient means of adding thi's attachment 

to recorders already installed on wells. As 

of 1960, the cost of construction was approximately $60.

The operation of the Drescher float-gage 

attachment can be best understood by following the action of the gage as the water level 

rises and lowers. (See fig. 4.)

As the water level rises the float is buoyed 

upward, thereby releasing tension on the float
METHODS OF INVESTIGATION

line (A ) and exerting less pressure downward 

on the idler pulley (B). The lever -arm assembly (C) with attached mercury switch (D) 

moves clockwise, as shown in figure 4 B . One 

of the contacts of the switch closes the circuit 

between the.battery (£) and motor (F ) t and 

the motor turns the reel (G ) clockwise, retrieving the float line. The recorder pulley 

(H) rotates and the water-level rise is recorded. When the float line has been retrieved 

an amount equivalent to the rise in water 

level, the motor tends to pull the float out of 

the water; the resulting increase in line tension causes the lever-arm assembly to move 

counterclockwise. The contact is broken on 

one side of the mercury switch, and the mechanism remains at rest until the water level 

changes again. The balance weight ( /) permits adjustment for the weight of the float 

and float line.

As the water level lowers the float is lowered, increased tension is applied to the float 

line, and the lever-arm assembly moves 

counterclockwise. The switch closes the electrical circuit and the motor-powered reel releases the float line until the water is supporting the weight of the float and the line 

tension is reduced. The lever-arm assembly 

then moves clockwise, causing the switch to 

open the electrical circuit, and the mechanism remains at rest until the water level 

changes again. Figure 5. Columbus cradle-gage attachment, A*, End view. B 

Side view.

COLUMBUS CRADLE-GAGE ATTACHMENT

The Columbus cradle-gage attachment is a 

revision of the standard water-level recorder 

that makes possible the recording of waterlevel changes in small-diameter wells. (See 

fig. 5.) It consists of a framework designed 

so that the recorder chassis itself tilts with 

a change in float position. The recorder, with 

attached control mechanism, is balanced on 

knife edges that are attached to a plastic base. 

Electrical contacts of palladium, which are 

equipped with spring-type overload protection 

and mounted on each side of the recorder 

frame close an electrical circuit as the recorder chassis tilts because of movement of 

the float and thus operate a motor-driven 

reel. The two-battery circuit has a switch 

for changing the direction of the recorder 

motion. An adjustable balance weight is attached to the recorder frame. The equipment 

is designed so that a water-level change as 

great as 3 feet per minute will be recorded.

A metal box encloses the recorder and all 

the control mechanism. The plastic recorder 

base described above is approximately 5 

inches above the bottom of the box, and the 

space below is utilized for battery storage. 

As of 1960, the cost of construction was approximately $200.

The operation of the Columbus cradle -gage 

attachment can be best understood by following the action of the gage as the water level 

rises and lowers. (See fig. 5.)

As the water level rises the float rises; the 

reduced tension on the float line (A) permits 

the recorder assembly to tilt counterclockwise, as shown in figure 5 A, thereby causing 

one set of electrical contacts (-B^, fig. 5B) to 

touch, complete the circuit, and actuate the 

motor-driven reel. The float line is retrieved 

over a pulley (C) and around the recorder 

pulley(D) that drives the recorder drum(E). 

The line is retrieved onto the reel ( f ) attached
EVALUATION OF EQUIPMENT FOR MEASUREMENT OF WATER LEVEL IN WELLS OF SMALL DIAMETER

to the motor (G), so located that a change in 

proportion of float line in the well or on the 

reel does not disturb the balance of the instrument.

As the float line is reeled in, the float is 

raised, and the increased weight on the line 

causes the recorder assembly to tilt clockwise. The previously closed electrical circuit is opened and the mechanism comes to 

rest.

As the water level lowers the float lowers; 

the increased tension on the float line causes 

the recorder to tilt clockwise until the other 

electrical contacts (B2 , fig. 5 B) touch, thereby 

completing the circuit. The motor-powered 

reel then releases float line until the line 

tension is reduced and the recorder tilts 

counterclockwise, opening the previously 

closed electrical circuit. The mechanism 

then will remain at rest until the water level 

changes again.

KOOPMAN FERRET-GAGE ATTACHMENT

The Koopman ferret-gage attachment may 

be used with any standard water-level recorder without modification of the recorder. 

(See fig. 6.) The gage consists of an 8-inchdiameter hollow aluminum reel and a 1-inchdiameter detector probe.

The compact reel encloses the relays,motor, and power supply (mercury battery) and 

stores as much as 750 feet of strong and durable 0.08-inch Ellsworth coaxial (armored) 

control cable. Although different response 

rates can be obtained by changing the ratio of 

the gear-drive assembly, the gearing ratio 

for the present reel was selected to permitresponse to water-level changes of 2 feet per1 

minute.

The detector probe is a streamlined unit of 

sufficient weight to maintain tension in the 

cable in spite of any dragging of the probe or 

cable against the well casing. The probe contains a single-pole, double-throw, center-off 

switch with attached swinging bar magnet, 

enclosed in a waterproof section of the probe. 

Below is a small float, in a section of the 

probe that is open to the water, on which is 

mounted a U-shaped magnet used to actuate 

the magnet switch above. As "of 1960, the cost 

of construction was approximately $250.

WATER-LEVEL-RECORDER PULLEY

ROTATION-SELECTION RELAY

MOTOR-CONTROL RELAY

B

Figure 6. Koopman ferret-gage attachment. A. Schematic.B. 

Front view, with reel cover attached.

The operation of the Koopman ferret-gage 

attachment can be best understood by following the action as the unit records a water-- 

level change.

As the water level rises the float in the 

probe is buoyed upward, and the opposition 

between the attached U-shaped magnet and 

the magnet on the lever arm of the switch 

causes the arm to swing in one direction and 

to close an electrical circuit, which in turn 

causes the motor to rotate the cable reel 

counterclockwise, as shown in figure 6B. The' 

direction of rotation is governed by the cur - 

rent that passes through the rotationselection relay in the cable reel and that in 

turn is determined by the presence or absence in the circuit of the direction-discrimination resistor in the detector probe. (See 

fig. 6 A.) The detector probe is thus retrieved 

until it reaches the new water level, at which 

t-imethe float returns to its original position, 

and reduction of the opposing magnetic force 

allows the switch lever arm to return to "off" 

position. The unit will then remain,at rest
METHODS OF INVESTIGATION

until there is another cnange in water level. 

The probe cable, passing around the recorder 

pulley, actuates the recorder to record the 

change in water level.

As the water level lowers the float in the 

probe moves downward, further reducing the 

force of the attached U-shaped magnet on the 

switch-magnet, and the spring-loaded switch 

lever arm closes the other electrical circuit. 

This causes the motor to rotate the cable 

reel clockwise and thus lowers the detector 

probe until the new water level is reached. 

The float then returns to its original position 

and causes the switch lever arm to return to 

the "off" position.

OTHER WATER LEVEL EQUIPMENT

Equipment and attachments, other than the 

three units just described, have been .studied; 

three types are described in general terms 

below.

The Keck immersion element probably is 

the first small-diameter sensing device that 

has a probe-activated rather than a float - 

activated float line. This equipment consists 

of a weighted probe suspended in the well by 

an electric cable that passes over the recorder pulley and is attached to a reel powered by a 6-volt motor. The probe consists 

of a pressure-sensitive switch encased in a 

flexible rubber membrane. As the water 

level rises or lowers in the well, the resultant change in pressure is transmitted by the 

membrane to the pressure switch. The 

switch, through the electric circuit, actuates 

the reel motor, and the probe is raised or 

lowered as required until it reaches a neutral 

pressure position at the new water level. 

The probe then remains at rest until the water level changes again.

Several models of the Keck immersion element were designed and constructed; the 

differences between models are mainly in the 

number of conductors in the electric cable 

used for the float line. Model KDC-1 has a 

3-conductor cable; model KDC-2 has a 2- 

conductor cable with an added relay circuit; 

model KDC-3 has a 1-conductor cable, the 

well casing serving as the other conductor.

The Criner gage attachment consists of a 

water-level-sensing probe attached to a 3- 

conductor cable that passes over the recorder 

pulley to a powered reel. The reel is powered by two 6-volt lantern batteries. Within

the probe, a mercury switch is connected by 

a linkage to a small float that tilts the switch 

as it responds to a change in water level. As 

the switch tilts, one side of an electric circuit is closed, and this causes the motorpowered reel to take in or let out cable until 

the probe reaches equilibrium at the new water level. When this position is reached, the 

probe remains at rest until the water level 

changes.

In 1954 the junior author contacted electronics manufacturers to inquire if they manufactured an electronic pressure-sensing device of small diameter. As part of the present 

project, renewed contacts with manufacturers 

indicated that at least 20 of them were producing pressure transducers. A pressure 

transducer is a device designed to convert 

pressure changes to changes in electrical 

current or voltage. A pressure transducer 

installed below the lowest water level expected in the well can be used to determine 

changes in water level by recording the 

change in pressure as the head above the 

transducer changes.

There are two principal methods of converting pressure changes to usable electrical 

data. .The amplitude-modulated system converts the output from the transducer to a 

proportional d-c voltage or current that can 

be recorded on such equipment as cathoderay oscilloscopes, strip-chart recorders, or 

magnetic oscillographs. The frequency-modulated system converts the output from the 

transducer into a proportional frequency that 

can be used on equipment such as magnetic 

tape recorders or frequency counters. Most 

transducers require demodulators or amplifiers in the electrical circuit to the recording 

equipment.

There are several primary types of pressure transducers, all having few moving parts 

(Berkley, 1958, p. 2-326 to 2-358). Some are 

of the variable-reluctance diaphragm type, in 

which the only moving part is a small metal 

diaphragm that moves only a few thousandths 

of an inch in an air gap between electromagnetic pole pieces. In the Bourdon tube-type 

transducer, the displacement of a Bourdon 

tube is transmitted directly to the moving 

contact of a precision wire-wound potentiometer, producing an electrical output proportional to the input pressure. With the 

strain-gage transducer, four strain gages are 

connected in a Wheatstone bridge circuit,
8 EVALUATION OF EQUIPMENT FOR MEASUREMENT OF WATER LEVEL IN WELLS OF SMALL DIAMETER

which is balanced at zero pressure all arms 

having approximately equal resistance. As 

pressure is applied, the grids of the strain 

gages are strained, with a resulting change in 

their electrical resistance, and the bridge 

becomes unbalanced. When an external fixed 

voltage is applied at the input terminals, this 

unbalance is reflected as a change in voltage 

at the output terminals that is proportional to 

the change in pressure.

EVALUATION OF EQUIPMENT

DRESCHER, COLUMBUS, AND KOOPMAN ATTACHMENTS

Many factors need consideration in the 

evaluation and selection of equipment for recording water-level changes in small-diameter wells. These factors are discussed in detail for the Drescher, Columbus, and Koopman 

gage attachments.

RECORDING ACCURACY

The ability of a gage attachment to transmit accurately a small water-level change in 

a well to a recorder chart is of primary concern. The principal factors affecting this 

accuracy are design of the float, float and 

float-line friction, sensitivity of the switching 

mechanism to movement of the float when 

water levels change, and the condition of the 

power supply.

The type and design of the small-diameter 

floats used in this evaluation (fig. 3) had a 

bearing on the accuracy of the Drescher and 

the Columbus attachments. The Drescher 

float-gage attachment gave the best results 

when equipped with a 1 3/8-inch plastic float 

of type H . Float types A , D , and C were next 

best, in that order. The Columbus cradlegage attachment comes equipped with a float 

of type B, but any of the small-diameter floats 

will work. All the floats, except types Fand 

G , will fit inside l|--inch pipe.

Float and float-line friction, or "drag," 

against the well casing greatly affects the 

recording accuracy of the Drescher and the 

Columbus attachments. For float-activated 

attachments of this type, this problem becomes especially acute in crooked or deep 

wells. The drag between the float and the 

well casing can be reduced by the addition of 

a light oil, such as kerosene, to the water 

surface. However, the largest error is not

caused by float drag, but by float-line drag 

along the well casing. Although small-diameter monofilament nylon line had less drag 

than other float-line material, it did not completely overcome the problem. The drag effects are more easily understood when it is 

realized that one of the small-diameter floats 

may have a total weight of only 6.5 ounces, 

and the weight added to or subtracted from 

the float line by a decline or rise of the water 

level would be only 0.2 ounce for an 0.1-fopt 

change.

When the Drescher and the Columbus attachments were carefully installed in the 

laboratory test tank or on a shallow well in 

the field, and the float line was prevented 

from dragging along the casing, their recording accuracy was approximately 0.02 foot. 

(See fig. 7 for an example of a Drescher-gage 

record.) As installed on the deep observation 

wells near Denver,Colo., and Madison, Wis., 

however, the gage attachments showed a pronounced effect from float and float-line drag. 

(See figs. 8 and 9.)

Figure 9 shows that the record of waterlevel fluctuations obtained by the Columbus

3.0

3.1

Ore: cher float-gag* attachment

3.7

12m 6 9 12pm 

TIME, IN HOURS

Figure 7. Comparison of water-level record from recorder with 

3-jr -inch-diameter float with record from similar recorder with 

Drescher float-gage attachment and 1^ -inch-diameter plastic 

float.
EVALUATION OF EQUIPMENT

O£O' Q

263.O 

263.2

j 1

Tape 

CharTop.

Chart

 1 

"

Tape -v

Tape

J

Tape

j-r 

1 Chart

Tap« 

Chjrt; i 

16 19 20 21 22 23 24 25

TIME, IN DAYS

Figure 8. Drescher float-gage record showing the effect of float 

and float-line "drag. *

72.S

72.7

72.8

72.6

72.7

72.

Standard water-level rec >rder 

with- 3 r/2 inch diameter f loot

* 4 I 1 

*

r/\J rtrttar V* ^^

Columbus cradle-gag 

attachment

30 31 Febl 2 3 4 

TfME, IN DAYS

Figure 9. Columbus cradle-gage record showing the effect of 

float and float-line "drag. *

cradle-gage attachment corresponds generally with that obtained by the standard waterlevel recorder. However, fluctuations of less 

than 0.02 foot are not discernible, and the 

record for February 3, 1959, is in error as 

much as 0.09 foot.

The Koopman ferret-gage attachment obtained records of water-level changes on 

wells of considerable depth with an accuracy 

of 0.01 foot. As shown in figure 10,the record 

of water-level changes obtained with this unit 

corresponds very closely to that obtained with 

a standard water-level recorder. The tendency to produce "steps" was not nearly as 

great as that with either the Drescher or the 

Columbus attachment. Thus, the principal 

disadvantage of the Drescher and Columbus 

attachments float and float-line drag and 

hang-up is not a problem with the Koopman 

ferret-gage attachment because .the weight 

of the detector probe overcomes the drag 

forces.

The sensitivity of the switching mechanism 

to the float movement also is very significant.

Koopman ferretgage attachment

3.7 i2m 6 9 12pm 3 6 

TIME, IN HOURS

Figure 10. Comparison of water-level record from recorder with 

3J--inch-diameter float with record" from similar recorder with 

Koopman ferret-gage attachment.

Both the Drescher and the Columbus attachments required about an 0.01-foot change of 

water level to raise or lower the float a sufficient amount to actuate the switches and 

drive the recorder. The Koopman attachment 

will respond to a water-level change of 0.005 

foot.

The condition of the battery power supply 

was critical. The accuracy of the Drescher 

and Columbus attachments was affected by 

weak batteries. When weak batteries were 

purposely used as the power supply for these 

two attachments, the record shown in figure 

11 was obtained. This record shows a poor 

response to water-level changes even though 

the response normally would be good for 

wells having such a shallow depth to water. 

To avoid this effect, the batteries -should be 

replaced after a maximum of 60 days of normal use.

The Koopman ferret-gage attachment also 

was affected by a power loss but much less 

than were the other two attachments, owing to 

a better float-to-switch response and to a 

longer peak-power life provided by the mercury-battery pack. The battery pack could, 

operate efficiently for approximately 90 days 

under normal conditions.
10 EVALUATION OF EQUIPMENT FOR MEASUREMENT OF WATER LEVEL IN WELLS OF SMALL DIAMETER

3.0

Columbus crodl«- 

gage atlachiment

Drcsctrar 

ag£ ottqchmwtt 

and l!6-inehdiameter plastic float

3.3

19 20 21 

TIME, IN DAYS

23

Figure 11. Effects of weak batteries on water-level records obtained by use of recorder equipped with the Drescher floatgage attachment, the Columbus cradle-gage attachment, and 

conventional 3 i-inch-diameter float.

RATE OF RESPONSE TO WATER-LEVEL MOVEMENT

The rate of response to water-level movement is determined by gear-drive and motorspeed ratios and also by an increase in the 

amount of power supplied to the motors. The 

Drescher float-gage, Columbus cradle-gage, 

and Koopman ferret-gage attachments had a 

rate of response to water-level movement of 

1, 3, and 2 feet per minute, respectively. The 

response rate could be safely increased to 2, 

6, and 4 feet per minute by gear-ratio 

changes. The response rate of the Drescher 

and Columbus attachments could be doubled 

again 4 and 12 feet per minute, respectively by doubling the power supplied to the 

motors. This increase, however, should be 

used only for short periods, such as during 

aquifer tests, because continuous operation 

at the higher voltage could injure the motors.

EASE OF REPAIR IN FIELD

Because of the possibility of a malfunction 

of a gage attachment and a resulting loss of 

record, the ease of repair in the field is a

significant factor. The Drescher and Columbus attachments are of simple construction 

and could be maintained and repaired by most 

field personnel with a minimum of instruction. The Koopman ferret-gage attachment, 

however, is more complex and, except for a 

battery change, could not be easily serviced 

or repaired in the field. Although the sealed 

design of this instrument makes it virtually 

trouble free, ^t probably would be necessary to 

maintain a spare attachment in the field to be 

used while a faulty unit was being repaired.

STABILITY UNDER INFLUENCE OF WEATHER

If the gage attachments are installed inside 

a recorder house,the effect of weather (temperature, humidity, and wind) is negligible, 

except for the Columbus cradle-gage attachment. With this attachment, temperature 

changes of only 10°F cause loss of sensitivity 

to water-level movement and even a shorting 

of the circuit, followed by battery failure. 

These effects are due to the design of the 

recorder framework, which is constructed of 

plastic, steel, aluminum, and brass sheets, 

all fastened together in such a mariner that 

difference sin expansion or contraction cause 

undue movement of the contact points.

The moisture in humid climates or dust in 

dry climates may injure the reel motors on 

the Drescher and Columbus attachments.

In the absence of a protective shelter, wind 

could cause considerable difficulty in the 

balance of both the Drescher and the Columbus attachments.

The Koopman ferret-gage attachment is 

completely enclosed and is not affected by 

any of these conditions.

EASE OF INSTALLATION

The Drescher and Koopman attachments 

are small and are simple enough that they 

can be installed with a minimum of effort and 

instructions. The time required for installation of either of these attachments would exceed only slightly the time required for the 

installation of a standard water-level recorder. The Columbus cradle-gage attachment is so designed that its size and weight 

(approximately 40 Ib) make installation somewhat difficult and time consuming.
EVALUATION OF EQUIPMENT 11

ADAPTABILITY TO STANDARD WATER-LEVEL RECORDERS

Although the Drescher attachment was designed to be used with the standard waterlevel recorder, it can be adapted easily to 

operate any water-level recorder that uses a 

horizontal-shaft pulley to drive the recorder 

drum. The Columbus cradle-gage attachment would require a complete new design 

before it could be used with any recorder 

other than the Stevens type F or FM. The 

Koopman ferret-gage attachment was designed to be used with any standard waterlevel recorder.

OTHER EQUIPMENT

The Keck immersion element was used 

with some success in several localities 

where the units could be closely observed 

and where personnel were proficient in maintenance and repair. Model KDC-1 proved to 

be the most satisfactory of the three models 

but had the disadvantage of requiring bulky 

and expensive 3-conductor cable. The rubber membrane of the immersion element 

and the insulation on the electric cable deteriorated rapidly, and the resulting leaks 

quickly shorted the electric circuit. These 

difficulties prevented universal acceptance 

of this device, and its development was discontinued. The device costs $50 to $100 to 

construct.

The Criner attachment offers a possibility 

for general use in all types of wells,because 

its motion is powered by a sensing probe. If 

the probe could be made heavier, effects of 

"drag" could be overcome; and the attachment would provide greater sensitivity than 

devices having larger floats. However, this 

attachment has several other disadvantages 

it requires bulky and expensive 3-conductor 

cable and a specially constructed mercury 

switch, and the mechanical connections within the sensing probe are subject to corrosion. 

This attachment probably costs between $50 

and $100 to construct.

Electronic pressure transducers are potentially promising for use in automatic recording of water-level movements in «malldiameter wells. Answers to questionnaires 

and personal interviews with many producers 

of transducers have been encouraging. An 

accuracy of at least 1 percent and as small 

as 0.5 percent of full scale can be obtained 

readily, and it is hoped that further development will provide even greater accuracy. 

Installation of transducer equipment by unskilled personnel would be virtually impossible, however. Transducers cannot be adapted 

to existing water-level recorders, and the 

cost of installation would be high. Excluding 

development costs, a transducer with digital 

read-out would cost approximately $1,000, 

and with recorder, approximately $1,500.

SUMMARY

The characteristics considered to be of the 

most importance in this evaluation are summarized in the table on the following page.

The Koopman ferret-gage attachment obviously is superior to the other gage attachments evaluated in this study. Its primary 

advantage is its ability to overcome drag and 

thus to record water levels accurately in 

deep or crooked wells. It is also more sensitive and efficient in recording water levels 

in shallow wells and in wells of small 

diameter.

Because of its simple construction, simplicity of operation, ease of maintenance, and 

low cost, the Drescher .float-gage attachment 

is good for use on wells where the water 

level is less than 50 feet below the land surface.

The pressure transducer offers considerable promise for future use in waterre sources work and its evaluation will continue. Its general application is limited by 

its high cost and complicated electronic circuits, but it does offer an accurate means of 

recording water-level changes in smalldiameter or crooked wells of great depth. In 

addition, transducers offer the intriguing 

possibility of recording water-level changes 

in observation wells at a considerable distance from a central-off ice recorder.
12. EVALUATION OF EQUIPMENT FOR MEASUREMENT OF WATER LEVEL IN WELLS OF SMALL DIAMETER

Evaluation summary for the Drescher float-gage, Columbus cradle-gage, and Kooproan ferret-gage attachments

Factors considered

Recording accuracy for depths 

to water of less than 50 ft ____________ feet___ 

Recording accuracy for depths 

to water of more than 50 ft. __________ feet___

Rate of response to waterlevel movement ___________ feet per minute. __

Approximate cfrsjt in 1960 _______ _ _ _ _ tfollars _ _ _

Ease of repair in field __ ______________________

Stability under 

influence of weather: 

Temperature ____________________________

Moisture ________________________________

Wind ...................................

Ease of installation __________________________

Adaptability to all standard water-level 

recorders _________________________________

Reliability under ideal conditions ______________

Simplicity of operation _______________________

Dreseher 

float -gage 

attachment

0.02

1

60

Good

Fair

Poor

Fair

Good

Good

Fair

Good

Columbus 

Cradle -gage 

attachment

0.02

3

200

Good

Poor

Fair

Poor

Fair

Poor

Fair

Fair

Koopman 

ferret -gage 

attachment

0.01 

.01

2

250

Poor

Good

Good

Good

Good

Good

Good

Good

REFERENCES

Berkley, Carl, 1958, Transducers, see, 2w 

in Cockrell, W. D., Industrial electronics 

handbook: 1st ed., New York, McGraw-Hill 

Book Co., Inc., p. 2-326 to 2-358.

Meinzer, O. E., 1937, The value of geophysical methods in ground-water studies: Am. 

Geophys. Union Trarvs., pt. 2, p. 385 387.

Stevens, J. C., [no date] Hydrographic data 

book: Leupold and Stevens Instruments, 

Inc., Portland, Oreg., 118 p.

INT.DUP..D.C.61-98 U 93