Crystal DTG User Manual

DTG Operation Manual

Introduction

Thank you for choosing the Digital Test Gauge (DTG) from Crystal Engineering
Corporation.

The DTG is very much like a mechanical test gauge:
Rugged, accurate, and easy to use. The difference,
of course, is the greater accuracy possible with
a digital display and, through an advanced
design, accuracy that is specified in percent
of reading over the entire operating
temperature range of -10°C (14°F) to
50°C (122°F).

The large LCD was designed to be
reliable and easy to see under a variety
of environmental conditions. The DTG
display is a full five digits (99999), so auto­ranging is not required: There’s always
enough display resolution for the rated
accuracy.

The silicon chip pressure sensors used in all DTGs are
highly repeatable over pressure and temperature. DTG
sensors incorporate a permanently filled, oil isolated
stainless steel diaphragm in an all-welded fitting. The only
wetted materials are 316 stainless steel. Integral to the
process connection is a stainless steel filter, insuring that only gases or liquids reach
the sensor diaphragm.

Other features include:

• Select from up to 9 different pressure units (depending on pressure range)

• Minimum and maximum pressure detection

• Automatic shutdown after 20 minutes (shutoff can be easily disabled)

• 1500 hour battery life (continuous use) on 3 standard alkaline AA batteries

Long battery life while maintaining high performance is the result of using a RISC
(Reduced Instruction Set Computer) type microprocessor. The case is electro­polished stainless steel with elastomeric seals, for weather and corrosion resistance.

And finally, the DTG is manufactured and serviced by a company that only makes
pressure measuring instruments. It’s the only thing we do and that’s why we say:

Pressure is Our Business!

PN: 2646 REV B, 8/2002

C R Y S T A L

engineering corporation

Firmware Release 1.05

Page 1 of 8

Operating Instructions

The DTG is shipped with batteries installed, so it’s ready to use. Press the power button and the
DTG will test all LCD segments. Continue pressing the power button for at least one second and
the DTG will start normal operation.

The DTG always resumes operation in the mode and the units of the pressure last used, and it

does not automatically rezero when turned on.

All DTGs are intended for gauge pressure measurement. That is, they indicate the difference
between applied pressure and ambient barometric pressure. The zero button can also be used
as a tare function, meaning it can be set to read zero pressure at for any pressure up to the full
scale of the gauge.

Connect the DTG to your system. Always use pipe thread tape or pipe thread sealant on the ¼″
NPT fitting. To ensure safe and accurate operation, please read the following warnings:

WARNING:

SEVERE INJURY OR DAMAGE CAN OCCUR THROUGH IMPROPER USE OF PRESSURE
INSTRUMENTS. Do not exceed recommended pressure limits of tubing and fittings. Be certain

all pressure connections are secured.

THIS GAUGE CAN DISPLAY ZERO PRESSURE WITH FULL SCALE PRESSURE APPLIED.

Do not rely on the display indication before disconnecting - it may not be indicating true pressure.

Never disconnect pressure instrumentation without first relieving system pressure.

CAUTION:

NEVER INSERT ANY OBJECT (other than the
CONNECTION. The sensor diaphragm is very thin and can be damaged or destroyed by solid

or sharp objects. Cleaning of the sensor must be done with appropriate solvents, only.

Zero/Tare

To make sure that the DTG is performing to it’s rated accuracy, the DTG should be exercised and
re-zeroed whenever exposed to changes in temperature (see Specifications). It’s also good
practice to check zero as your final reading too, as the DTG should return to a perfect zero
reading. (If it does not return to zero - check the filter - it may be blocked).

The DTG can zero (or “tare”) any applied pressure within it’s specified operating range.

This means that even if zero pressure is displayed, the actual gas or fluid pressure connected to
the DTG may be high enough to be dangerous if you were to disconnect the DTG without
relieving the pressure first.

ambient pressure before disconnecting the DTG!

To zero or tare the DTG, you must press the Zero button for at least one second before it
responds.

This is to avoid unintentional changes to the zero/tare setting.

Always check that the pressure has been equalized with

Over-pressure Conditions

The DTG will read pressure up to approximately 110% of the rated pressure range, at which
point the display will start flashing and the readings will not be reliable. The zero function does
not affect the point at which the display starts flashing to indicate over-pressure, so depending
on the tare value it is possible that the display can start flashing without the maximum pressure
being displayed.

For instance, if a 100 PSI DTG is zeroed when 30 PSI is being applied, it will indicate that the
over-pressure condition has been reached at 80 PSI (i.e., 110% x 100 PSI – 30 PSI = 80 PSI).

Over-pressure can affect accuracy, but the effect is only temporary unless the sensor has been
destroyed. See Specifications on for maximum over-pressure.

(The one second delay avoids turning on the DTG by mistake.)

1

⁄⁄

″ ″

⁄16

″ NPT metal filter) INTO THE PROCESS

⁄⁄

″ ″

PN: 2646 REV B, 8/2002
Firmware Release 1.05
Page 2 of 8

TM

PRESSURE is Our BUSINESS

Units button

Pressing this button causes the DTG to select the next unit of pressure measurement. There are
up to 9 units available. See Specifications on page 5 for the list of scales.

Peak detection

The DTG continuously records maximum and minimum applied pressure, and cannot be
disabled. To view the maximum pressure value press the PEAK button. Press the PEAK button
again to view the minimum recorded pressure. Pressing the PEAK button once more returns the
display to the current applied pressure reading.

Resetting recorded peak values

When displaying either high or low recorded pressure, the zero button is used to reset the peak
high and low values to the currently displayed pressure. This will not affect the zero or tare
value. If you need to rezero the gauge, the gauge must be in normal pressure mode.

Automatic shut-off

Normally, the DTG will turn off automatically after 20 minutes of operation without a key
depression. This can be defeated however, when turning the DTG on. Pressing the ON/OFF
and ZERO buttons simultaneously will prevent the DTG from automatically turning off. The DTG
will briefly display the words “No Auto Off” to indicate that it will not turn off.

This procedure is required each time the DTG is turned on, if you want to defeat the auto­shutoff.

Low battery indication

A lighted battery icon is the first indication of a low battery. The DTG will continue to operate
accurately while the icon is lit. When the batteries are exhausted, the letters “batt” will appear
across the display and no further pressure measurements will be possible until the batteries are
replaced.

Battery replacement

The DTG uses 3 AA batteries. Alkaline batteries are recommended, but not required if the
gauge will only be operated in warm environments. Most alkaline batteries will operate down to
–10°C or colder.

Figure 1: Remove Trim Ring

Remove the trim ring on the front of the DTG (Figure 1) by
rotating it counter-clockwise. Then remove the four #6
screws from the back of the DTG as shown in Figure 2.

Carefully separate the front of the DTG from the housing.
Be careful to not put stress on the cable between the
sensor and the circuit cards. When replacing the batteries
be sure to install them in the indicated orientation.

Figure 2: Four Access Screws

C R Y S T A L

engineering corporation

PN: 2646 REV B, 8/2002

Firmware Release 1.05

Page 3 of 8