Ashcroft a4a 설치 및 유지 관리 매뉴얼 - 페이지 9

{카테고리_이름} Ashcroft a4a에 대한 설치 및 유지 관리 매뉴얼을 온라인으로 검색하거나 PDF를 다운로드하세요. Ashcroft a4a 20 페이지. Precision pressure gauge

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imized or eliminated through the use of commercially avail-

able pressure snubbers.

When the application for which the gauge is to be used

involves the sudden release of pressure, the "Slotted Link"

option should be specified at the time of order to protect the

movement assembly.

Temperature Error

Ashcroft A4A gauges are typically used where tempera-

tures are maintained within close limits. In cases where

extreme temperature variations will be encountered, correc-

tions may be calculated and applied to the gauge readings.

When temperatures rise the Bourdon tube reads faster and

when they drop it reads slower at a rate of one percent per

50ºF. In these cases, the automatic bimetallic thermal com-

pensation option is recommended for greater accuracy and

convenience. When equipped with the bimetallic compen-

sator, the gauge accuracy will be maintained through tem-

perature from -25ºF to +125ºF.

Loose Pointer

Gauge error may be caused by a loose pointer. If pointer

shift is suspected, simply release pressure and check that

the pointer returns to the zero position. If an adjustment is

necessary first position the zero adjust mechanism in the

middle of its full range of adjustability. Once this is accom-

plished, move the pointer to the proper position and, using

your fingers, press it firmly onto the shaft. The pointer

should never be hammered or tapped in place.

5.0

CALIBRATION

5.1

CALIBRATION STANDARDS

In order to properly check and adjust the calibration of a

precision gauge, a reliable standard of reference is

required. Care should be taken in the selection of a dead-

weight tester since the resulting operation of the precision

dial gauge can be no more accurate than the standard on

which it is based.

A primary pressure standard with accuracy of ±0.025 per-

cent of reading or better is recommended to properly check

or calibrate the Ashcroft A4A. Corrections for local gravity

effects, air buoyancy and temperature should be applied to

the pressure standard to compensate for environmental

conditions.

Note: If a secondary transfer standard is used, it should be

of the same range as the instrument being tested and have

accuracy of ±0.025 percent of span or better.

If you would prefer, NIST traceable recalibration of your

Ashcroft A4A Precision Pressure Gauge can be performed

at the Ashcroft Inc., Stratford, CT facility. Priority Recertifica-

tion can be arranged to assure the gauge is calibrated and

shipped for return to your facility within 5 days of receipt at

the Stratford Operation. Contact Ashcroft Inc. Customer and

Support Service at (203) 378-8281 for further details on

available calibration services.

5.2

CALIBRATION CHECK

Apply full pressure on the gauge for several minutes and

then release the pressure. Re-zero the gauge, if necessary.

Using an appropriate pressure standard generate pressures

and take readings at zero to full scale in 10% increments,

both upscale and downscale. If the error exceeds the

amount permissible for the intended service, follow the

recalibration procedure (Section 5.3).

5.3

RECALIBRATION PROCEDURE

Prior to beginning calibration on a fluid media the Bourdon

tube must be completely free of entrapped gas or, if calibra-

tion is to be done on a gas system, the Bourdon tube must

be free of any liquid.

5.3.1

Linearity Test

Step 1-

Load the gauge to full scale pressure and return to zero.

Step 2-

Adjust the pointer to zero with the dial centered. If neces-

sary, remove pointer then center the zero adjust mechanism

and replace pointer.

Step 3-

Load the gauge to one-half scale pressure and record the

reading.

Step 4-

Load the gauge to full scale pressure and record the read-

ing. If linearity is normal, the reading at full scale pressure

should be double the reading at one-half scale pressure so

as to produce a straight line relationship.

If the readings are not linear, recalibration procedure as fol-

lows is indicated:

5.3.2

Linearity Adjustment

Step 1-

First the gauge must be "straight lined". That is to make the

readings linear or proportional to the load. At this point the

actual value of the readings at any given load is secondary.

Once linearity has been established, range adjustment to

bring the full scale reading into agreement with the full scale

load will complete the calibration.

Unscrew the zero adjust locking knob and remove the two

knobs and then remove the bezel and window by lifting the

bottom up and away from the gauge face.

Step 2-

Remove the back blow out cover by unscrewing the knurled

knob on the center back of the gauge and lifting away the

stainless steel blow out disc.

CAUTION:

Prior to proceeding it is recommended that the tooth rela-

tionship between the sector and its mating pinion be

marked (see figure 5.1). If the sector and pinion are acci-

dentally disengaged these marks will assist in proper re-

engagement. For optimum performance the original tooth

engagement should be maintained.

Step 3-

To compensate for a full scale reading greater than twice

the one-half scale reading:

Consult Figures 5.1 & 5.2

Loosen the two clamping screws on the quadrant slide and

slide it upward, thereby decreasing the angle. Or, if the error

is slight, rotate the pointer and pinion shaft counter clock-

wise to indicate about twice the extent of the error. Holding

the pointer in this position, release the quadrant clamp

screw permitting the Bourdon tube to adjust its position,

then re-clamp. This also results in a decrease in angle.

To compensate for a full scale reading less than twice the

one-half scale reading use the same procedure outlined in

step 3 except as follows: