Crystal DTG - Manual (Page 4)

PN: 2646 REV B, 8/2002
Firmware Release 1.05
Page 4 of 8
PRESSURE is Our BUSINESS
TM
Other display conditions
All decimal points lit simultaneously is an indication of an internal problem or failure.
Reset
If, for some reason the unit needs to be reset, remove any battery for at least one minute, then
reinstall the battery. If the reset is successful, the DTG will start operating without pressing the
ON /OFF button.
Measuring Vacuum
All versions of the DTG can be used to measure moderate vacuum. When measuring pressure
less than ambient barometric conditions, a minus (-) sign will appear. DTGs are not recom-
mended for continuous use at high vacuum (pressures less than -14.5 PSI, at sea level).
Digtal Interface
The DTG can be connected to standard RS-232 computer ports. This requires an accessory
cable/interface adapter and software available from Crystal Engineering.
Calibration
If adjustment is required, we recommend returning the unit to the factory.
Factory service offers benefits you won’t find anywhere else. We have the facilities to provide
calibration reports that include test data at a variety of temperatures utilizing NIST traceable
standards. In addition, upgrades may be available to add or enhance operating features. We
designed the product to last, and we support it so that you can get the most from your invest-
ment.
We recommend the DTG be recalibrated on an annual basis. However, your quality system
requirements may require more or less frequent calibration depending on the environment in
which it is used, and the calibration history of your DTG.
Although we prefer that you return the DTG to Crystal Engineering for calibration, ordinary
recertification and/or adjustments may be performed by any qualified personnel with appropriate
training and equipment. The following instructions are ONLY intended for such qualified
personnel with appropriate test equipment. We recommend that the calibration standards
used have a minimum rated accuracy of 0.025% of reading, or equivalent in terms of percent of
full scale. Usually, this level of accuracy requires the use of piston (deadweight) gauges or very
high performance pressure controllers, such as those manufactured by DH Instruments
(www.dhinstruments.com).
There are no internal potentiometers: The DTG contains a “span” factor which all readings are
multiplied by. Normally, this is set to a value of 1.0000. However, as components age this may
need to be changed to a value slightly higher or lower than 1. This adjustments is made via the
keypad or the RS-232 interface. If adjustment is required, determine the span factor that results
in the best fit of the data to the true pressure applied.
“Zero” the DTG, then record readings for at least two or more pressure points. Determine if the
DTG needs, or would benefit from, a change in the span value.
To change the span factor, turn off the DTG, then press the ON, UNITS and PEAK buttons
simultaneously. The word “cal” will briefly be displayed, followed by the actual span value. The
span factor may be adjusted by pressing either the units button (to increase the value) or peak
button, to decrease the value. The value changes in 0.0001 increments. Press the ZERO button
to store the new value in memory.