Ashcroft 2279 - Duratran® Pressure Transmitter - Manual (Page 2)

CALIBRATION
If it is necessary to rezero the instrument, (i.e. to correct for
head effect in the piping), this may be done by removing the
front ring and window. The indicating pointer is set by the
micrometer adjustable hub. Zero and span adjustments are
accessible from the front through holes in the dial; use a small
screwdriver for this. The case should only be opened in a dry
and clean environment, preferably in an instrument shop.
Complete recalibration may be required after extended service
or if the instrument has been overpressured.
Calibration should be checked against a test gauge and pres-
sure source, or a deadweight tester, appropriate to the range of
the transmitter. ANSI B40.1, “Gauges – Pressure Indicating Dial
Type – Elastic Element,” recommends that the pressure stan-
dard be at least four times as accurate as the instrument being
tested. A power supply and milliameter, or voltmeter and resis-
tor, of suitable accuracy are also required to test the transmitter
output. These are to be connected in series with the output
leads, observing correct polarity, as in Figure 1.
With the input pressure at zero, the micrometer pointer adjust-
ment and the “zero” potentiometer should be adjusted for zero
indication and 4mA output respectively. The pressure should
then be raised to full scale and, if the output is not 20mA, the
“span” potentiometer used to correct the span error. The zero
should then be rechecked. If an indication span error is found, it
is necessary to open the back of the case and adjust the slide.
More information on indicator calibration is available in Ashcroft
Maintenance and Repair Manual. visit www.ashcroft.com for the
most up to date version. When the indication span and zero are
correct, replace the back of the case prior to final calibration of
the transmitter. Caution: do not adjust the “zero” and “span”
potentiometers while the back of the case is open; ambient
light may cause erratic results. Mechanical zero/span adjust-
ment should normally not require any electrical adjustment.
The front window and rear cover must be firmly and evenly
tightened to prevent moisture or corrosives from damaging
the circuit board.
Installation and Maintenance Instructions for
ASHCROFT ® Type 2279
Duratran ® Pressure Transmitter
© 2007 Ashcroft Inc., 250 East Main Street, Stratford, CT 06614-5145, USA, Tel: 203-378-8281, Fax: 203-385-0499, www.ashcroft.com
All sales subject to standard terms and conditions of sale. I&M00810043-9/01 (Form No. 250-2598) Rev. 10/12