Operator’s guide to the Ealey Digital Tape

Extensometer

General description.

The digital tape

extensometer is used to

measure any change in the

distance between two fixed

points, which are attached to

the structure, building or

tunnel to be monitored.

By measuring the change

in the distance between any

number of fixed points

arranged in a pattern, it is

possible to indicate the type

and amount of movement

effecting the structure, building or tunnel being monitored. By using the same fixed points to

locate a levelling staff or EDM target, it is possible to incorporate tape extensometer data

into a more comprehensive monitoring survey.

The tape extensometer system consists of a steel tape punched with holes at regular

intervals which is stretched between two eye bolts (the fixed points) and tensioned by the

instrument. The instrument has two purposes, to apply a consistent tension to the tape and to

provide an accurate measurement of the distance from the punched hole in the tape to the eye

bolt being measured.

The digital tape extensometer operates by applying tension to the tape by retracting the

sliding bars on which the locating pin block is mounted. A tension sensing device indicates

when the bars have been retracted sufficiently to apply the correct tension, and a digital

measuring device directly connected to the sliding bars provides an accurate reading of the

distance from the punched hole being used to the eye bolt.

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To take a reading

There is no on/off switch for the tension sensing device which operates automatically,

ensure that the battery holder contains a charged 9 volt battery before commencing and that

the digital gauge is on. If the gauge is off, the automatic on / off zero retention function will

switch it on the moment the handle is turned to take a reading. Make sure that the display

reads 0.00mm when the winding handle is turned clockwise until it will turn no more (it will

come to a natural stop, do not force the handle) before commencing. See the "care of the

instrument" section for further details.

1. Turn the winding handle anti-clockwise until the sliding bars are fully extended, the

gauge should read at least 55mm.

2. Hook the tape onto the first eye bolt and the instrument onto the second eyebolt.

3. Pull on the tape so as to remove as much sag as possible, place the nearest punched hole

over the locating pin and secure with the clip.

4. Support the instrument with your left hand and turn the winding handle clock-wise until

one or both of the indicator lights comes on. Turn the winding handle back a small amount

until both lights go off.

5. Turn the winding handle clock-wise in small stages until only the green indicator light is

on when the instrument is at rest and not being touched by the operator.

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6. Place a finger under the tape as shown in figure 2 and gently lift the tape so as to relieve

a small amount of the tension on the tape, the green light should go off. By gently removing

the finger the green light only should come on again, if the light stays off turn the handle

clockwise a small amount until enough tension is being applied that the green light goes on

and off again with the gentle placing and removing of the finger under the tape.

7. Should the red light come on, the instrument is over tensioning the tape and you should

return to stage 4, alternatively, it may be that you are not being gently enough with the

placing and removing of your finger remember, as with any other item of survey

equipment the results are only as good as the care you take in getting them.

8. Once you are satisfied that the correct tension is being applied, you may note the reading

on the digital gauge. Should you have to turn or move the instrument to note the reading the

red light may come on or the green light go off, do not worry, once the correct tension is set

the gauge is locked until you next touch the handle. Take care not to touch the winding

handle until you have noted the reading.

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9. The value of the reading is simply the distance along the tape to the punched hole used

plus the digital gauge reading.

Example; pin hole at 3.75m, gauge reading 28.25mm, total reading = 3.77825m. The tape

commences at 500mm, and as this is the same as length of the instrument there is no need to

take into account the length of the instrument.

10. Turn the winding handle anti-clockwise until the sliding bars are fully extended and

remove the tape from the locating pin. The instrument in now ready to take the next reading.

Care of the instrument

1. The instruments working life will be extended if care is taken to keep the instrument

clean. If the instrument has been exposed to dirt or dust, wipe it clean with a soft cloth at the

end of each day, paying particular attention to the sliding bars.

2. Store the instrument with the sliding bars retracted so that the gauge reads between 3mm

and 5mm. The 9 volt battery may be removed if the instrument is to be stored for any length

of time. The 9 volt battery holder is located on the rear face of the casing. In order to

preserve the life of the digital gauge battery the gauge the instrument will automatically

switch off when it has not been used for a few minutes.

3. The digital gauge is operated by an internal battery, which has a life of up to one year in

normal use. A figure small B will appear on the display when the battery is low. The digital

gauge battery is automatically replaced every time the instrument is serviced. Do not attempt

to change the battery yourself as this may result in damage to the gauge and loss of

calibration. The manufacturer accepts no responsibility for any damage caused if you

attempt to change the battery yourself, always return the instrument to your supplier if

you require a new battery.

4. The instrument has an automatic on / off and zero retention function which removes the

need for the operator to switch on or off or zero the instrument. The instrument is fitted with

two buttons, on and zero. They may be operated with a small object such as the point of a

ball point pen. These buttons should not normally be operated unless it becomes necessary in

the unlikely event of the instrument not automatically switching on. The operator should not

press the zero button unless the instrument is fully retracted.

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5. The instrument should be returned to your suppliers at least once a year for service and

calibration, or more frequently depending on the amount of use it is subjected to. The

instrument may be returned for a calibration check and the issue of a new calibration

certificate at any time.

Useful hints on operating your Ealey digital tape extensometer

1. Always store the instrument with the sliding bars extended by 3mm to 5mm as

recommended in section 2 of care of the instrument as this will prevent damage to the

instrument should the operator forget which direction extends the sliding bars.

2. The red light that indicates when the tape is over-tensioned, is set to illuminate at

between 0.2mm and 0.3mm after the green light. Over long distances, 15m or more, tape

flutter may cause the red light to come on too soon. If this is the case, just return the

instrument to your supplier for adjustment or specify the distances to be measured at the time

of purchase.

3. As with any other type of tape extensometer, the travel on the instrument is slightly

greater than the pitch of the punched holes. As a result, it may be possible over some

distances to take readings on two holes. Example; 4.25mm or 54.25mm. To avoid this it is

recommended that you always fully extend the sliding bars before commencing each reading.

4. Always set up at least two test readings in locations well away from the effected area,

but preferably under the same type of conditions, in order to have an on-site check on the

calibration of the instrument. Take and note these readings at the beginning and end of every

survey. Any gradual variation in the results will provide an indication of the likely need for a

service or re-calibration of your instrument.

5. The location of the punched holes in the tape may not appear to align with the

printing of the tape. This should be ignored as the punching of the holes is carried out using a

special machine to make the tapes interchangeable. Use the nearest 50mm dimension as the

reading on the tape, 1.5m, 1.55m, 1.6m, 1.65m etc.

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6. When setting up your test points, first of all, practice with your instrument until you are

happy that you are achieving good repeatability, then take a number of readings, say 10, and

average the results. When you have decided on your average reading, note it and take one or

two more to check, a mistake in your test reading could plague your survey for months.

7. Always take two sets of base readings for your monitoring survey, once movement has

occurred errors will be impossible to identify.

8. Always ensure that your monitoring survey extends to a point outside of the area likely

to be effected, your design staff will not be pleased if you cannot tell them where movement

is not occurring as well as where it is.

9. Always make a careful note of the instrument and tape serial numbers when

commencing a set of readings.

10. Note down and keep a careful check on the temperature during the taking of a set of

readings. In tunnels, do not assume that the temperature remains constant during the time of

your work or that it remains constant along the length of a tunnel. The coefficient of thermal

expansion as supplied by the manufacturer of the tapes is 10.2 x 10 – 6/Cº. It is

recommended that you use your test points to check the thermal expansion

11. The manufacturer of the Ealey digital tape extensometer aims to provide technical

support for instrument users. They will be pleased to provide any help they can and discuss

any modifications to the instrument that may make it usable for your particular survey.

Changing the tape

To change the tape, wind the tape up fully and then grasp the tape and spool in one hand and

with the other hand turn the tape winding handle anti-clockwise in order to unscrew it from

the spool. Remove the old tape, put another tape in place and screw the handle into the spool

of the new tape.

Copyright; P.J.Ealey (Engineering) 2004. (01424 423393) vM42