Cooper Instruments & Systems DPG 100 Digital Pressure Test Gage - Manual (Page 17)

5.3.5 4-20 mA Output Option
Figure 5-6: Wiring code for 4-20 mA output option
5.4 Explanation Of Limits
Limits allow the instrument to signal both the operator (via the front panel indicators) and other equipment (via the
contact relays) that the pressure is within or outside of a specified range. Limit 1 is a "low limit" and Limit 2 is a
"high limit."
If the pressure applied to the instrument is less than the setpoint entered for Limit 1, the limit will turn "on." That is,
the LED indicator on the front panel will illuminate,
the normally open relay terminal for Limit 1 (L 1-NO) will be connected to its common terminal (L 1-COM),
and
the normally closed relay terminal (L 1-NC) will no longer be connected to its common terminal (L 1-COM).
When the pressure rises above the Limit 1 setpoint plus 1% of the range of the instrument, the limit will turn "off."
When Limit 1 is turned "off,"
the LED indicator on the front panel will not be lighted,
the normally open relay terminal for Limit 1 (L 1-NO) will not be connected to its common terminal (L 1-
COM), and
the normally closed relay terminal (L 1-NC) will be connected to its common terminal (L 1-COM).
The 1% specification given above is the "hysteresis" or "deadband" of the J Series instrument limits. Hysteresis
prevents the limits from chattering on and off when the pressure is slowly moving through the limit setpoint. For
example, if the low limit setpoint is 100 PSI and the range of the instrument is 500 PSI, then Limit 1 will turn on
when the pressure drops below 100 PSI and Limit 1 will turn off when the pressure rises above 105 PSI.
Correspondingly, Limit 2 (the "high" limit) will turn "on" when the pressure rises above its setpoint, and turns "off'
when the pressure falls below the setpoint minus 1% of the range of the instrument. For example, if the high limit
setpoint is 2000 PSI and the range of the instrument is 3000 PSI, the Limit 2 will turn on when the pressure rises
above 2000 PSI and Limit 2 will turn off when the pressure drops below 1970 PSI.
5.5
Entering The Limit Setpoints
To change the limit setpoints with the Setup Menu, see "FIELD SELECTABLE FEATURES" in Chapter 6.
5.6 Trimming Of Analog Outputs
Occasionally, the instrument's analog output signal (4-20 mA or 0-5 VDC) may need to be adjusted. The following
sequence should be followed by anyone wishing to trim their analog output. The front display of the instrument
should be calibrated (see "CALIBRATION" in Chapter 4. Before attempting to adjust the analog output. A calibrated
standard is required to calibrate the front display, but no pressure source is needed to adjust the analog output.
DPG 100 14 Rev Feb 2001