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計測機器 Ashcroft a4aのPDF インストレーション＆メンテナンス・マニュアルをオンラインで閲覧またはダウンロードできます。Ashcroft a4a 20 ページ。 Precision pressure gauge

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If damage is observed consult factory for further instructions.

Ashcroft A4A gauges are shipped with a small piece of

plastic sponge between the pointer hub and the inside of

the glass. This prevents the pointer from "whipping" during

shipment. When your new gauge is unpacked, this cushion

should be removed and discarded.

To remove this cushion first remove the inner small chrome

knob at the bottom of the bezel by unscrewing it in a coun-

terclockwise direction. Next lift the bottom of the bezel and

slide it off the upper hinge pin.

Note: When replacing the bezel gently turn the outer dial

adjustment knob (large chrome knob) to assure that the

gear teeth on the adjuster mesh with the rack on the dial.

All Ashcroft A4A gauges are accurately calibrated to ±0.1%

of full scale or better, against standards that are traceable to

the National Institute of Standards of Technology. A certified

copy of test results is furnished with each gauge. Standard

conditions for calibration conform to NIST Monograph 8.

To check gauge accuracy after unpacking, follow instruc-

tions in Section 5.0 – Calibration.

Important Information

Gauges for use with corrosive or hazardous media such as

mercury or radioactive solutions should be tested with a

non-corrosive non-hazardous medium such as air, water or

oil prior to acceptance. Faults found after an instrument has

been contaminated will be the sole responsibility of the user.

Contaminated instruments may not be returned to the facto-

ry without written authorization. Failure to obtain authoriza-

tion may inadvertently result in injury to Ashcroft Inc. per-

sonnel and/or property damage. Contaminated gauges

returned without prior written approval will be returned to

the sender unrepaired.

3.2

INSTALLATION

*** WARNING ***

Where the gauge is to be used with oxygen, it should be

clearly specified and the gauge will be so marked either on

the dial for 8

⁄

, 12 and 16 inch gauges or on the back of the

gauge for the 6 inch dial size. In these cases, special pre-

cautions are taken to eliminate all traces of organic matter

which might otherwise cause an explosion hazard.

The gauge should not be used with elements or com-

pounds deleterious to the wetted materials.

Gauges are factory calibrated in an upright or vertical posi-

tion, unless otherwise specified on the order. Gauges

should always be mounted in the same position as calibrat-

ed to eliminate possibility of positional error. If gauges are to

be mounted in other than vertical position the order should

specify the angle in which to be mounted to permit factory

calibration in the same position.

Mounting dimensions are given in the dimensional drawings

and charts in Appendix C.

4.0

OPERATION

All Ashcroft A4A pressure gauges are precision instruments

and certain precautions must be observed in their operation.

4.1

BLEEDING THE SYSTEM

The gauge should be mounted in an upright position when

connected to a liquid pressure system and the bleeder

(flushing connector) should be operated before readings are

taken. Accurate readings on a liquid pressure system are

impossible unless all air or other gas has been evacuated.

All Ashcroft A4A gauges are equipped with a bleeder valve

(flushing connector) as an integral part of the Bourdon tube.

When operating the bleeder valve (flushing connector) sup-

port the free end of the Bourdon tube with fingers to prevent

disengagement of the gear teeth or possible bending of the

link or tip piece. To operate the bleeder, the valve is opened

slightly and pressure applied to the gauge to force fluid

through the tube and out the valve. To avoid getting fluid in

the movement assembly it is recommended that a tube or

some type of shield be used to direct the liquid flow away

from the gauge case and movement. Since some oil may

have accumulated near the bleeder valve tube after factory

calibration, the fluid should be permitted to flow for several

seconds. Any air or gas present in the gauge should then

escape followed by a steady flow of the pressure medium.

The bleeder may then be closed.

It is good procedure to apply full pressure on the gauge for

several minutes before each period of use. The pressure

should then be removed and the dial zero adjusted, if nec-

essary.

4.2

SETTING DIAL TO ZERO OR TARE OR VALUE

All Ashcroft A4A gauges are equipped with a dial adjuster

and friction brake. The dial adjuster is operated from the

front cover of the case and moves the dial – not the pointer

– through approximately 30 degrees of rotation. This adjust-

ment is used to set zero, tare out a pressure pre-load or,

with absolute gauges to set the pointer to the prevailing

barometric pressure. In tests involving an initial pressure

which is ordinarily carried through the calculations as a tare,

resetting of the dial will simplify the calculations by eliminat-

ing the tare figure entirely.

4.2.1

SETTING DIAL TO PREVAILING BAROMETRIC

PRESSURE (ABSOLUTE GAUGES ONLY)

The dial adjuster is also used to allow an A4A gauge to sim-

ulate the performance of an absolute pressure gauge. To do

this the gauge operator must determine the prevailing baro-

metric pressure from an accepted source (such as an in-

house barometer or a nearly airport). Once this is known

the operator, using the dial adjuster, rotates the dial so that

with the gauge connection vented to atmosphere the point-

er is directed to the prevailing barometric. Once this is

accomplished, the external adjustment locking nut should

be tightened. With the pointer set to barometric pressure

prior to connecting the process connection to the pressure

input the gauge will measure pressure in terms of absolute

pressure. Periodically, to adjust for changing barometric

pressure, the process connection of the gauge must be

vented to atmosphere and the dial adjusted to display the

prevailing barometric pressure.

4.3

GENERAL OPERATING CONSIDERATIONS

The Ashcroft A4A gauge is "Test" or "Master" gauge and if

properly cared for should retain its inherent accuracy indefi-

nitely. However, where gauges are used for highly critical

work over a long period of time, it is good practice to check

them at regular intervals against a deadweight tester. The

procedure for testing and adjusting is given in Section 5.0.

Pressure Surges

Utmost precaution must be taken at all times to protect the

gauge from high pressure surges or shocks. The sudden

application or removal of pressure will cause the pointer to

whip around and, by its inertia, to damage the movement,

or may move the pointer on its shaft. This effect can be min-