Teledyne HASTINGS 2002, Instruction Manual, Page: 11 / 49

page 11
3.3 High and Low Set Point Modes
The Model 2002 provides TTL outputs for process control. The I/O cable is attached via a 7-pin
circular DIN connector to the rear panel of the control unit. The pinout is shown in Figure 2.1.
To view the high set point, place the Model 2002 in the HIGH mode by pressing the mode switch
to illuminate the HIGH light and no other mode light. The display will show the set point selected.
There is no hysteresis (dead band). During normal operation the alarm light will trigger and the
TTL output (pin # 3) will go high (+5 V) if the pressure exceeds the set point.
Similarly, to view the low set point access LOW mode by pressing the mode switch until the LOW
light is lit and no other mode light is illuminated. During normal operation, the LOW light will light
and the LOW alarm TTL output (pin # 4) will go high (+5 V) if the pressure becomes less than
the set point.
The alarm lights cannot indicate an alarm condition while in the set point modes. Therefore, it is
advisable not to leave the instrument in these modes for extended periods.
To adjust a setpoint, press the mode switch until the sepoint is viewed then simultaneously press the
UP and DOWN arrow keys. The active mode light will now flash indicating that the interlock has
been bypassed and the setpoint can be adjusted. The display shows the present set point.
Enter the new set point by using the blue circular up and down arrows. Press and hold the up
arrow to increase the set point and the down arrow to decrease the setpoint. Allow several seconds
for the circuitry to respond. If the button is held down for and extended period of time the adjust-
ment rate will start to increase. Release the button and press again to get finer control of the exact
trigger point.
At this point, the new set point is in temporary memory. If the instrument were unplugged now,
the Model 2002 would revert back to the original set point upon restarting. Return the 2002 to the
RUN mode to store the set point in permanent memory.
Once the interlock has been bypassed in either set point mode it will stay active in the following
modes until the GAS mode is entered. This will allow the user to set both setpoints and adjust the
calibration without repeating the interlock bypass.
3.4 CAL Mode
Optimal performance of the Model 2002 is achieved by performing in situ adjustments to the
calibration coefficient in the CAL mode. There are three calibration coefficients. These are the
zero coefficient, the midrange coefficient and the atmosphere coefficient. Once a tube has been fully
calibrated the midrange coefficient should never need further adjustment, but it may be helpful to
adjust the zero coefficient or the atmosphere coefficient under certain situations. Even though the
operator inputs may be identical for adjustment of all three coefficients, the power supply / display
will detect the power level of the tube and adjust the proper coefficient for pressure level of the
adjustment.
Points that should be noted before adjusting the calibration . The first one occurs when
attempting to adjust a calibration coefficient by using the blue circular up and down arrows.
Press and
hold the up arrow to increase the displayed value and the down arrow to decrease the
displayed value. When the button is first pressed, the displayed reading may jump in the opposite
direction expected. This is normal and is caused by the temperature compensation routine resetting
to the current temperature. Allow several seconds for the circuitry to respond. If the button is held
down for an extended period of time the adjustment rate will start to increase. Release the button
and then hold again to regain finer control of the displayed number.
Another point to be noted is the fact that after the adjustment, the new calibration coefficient is only
in temporary memory. If the instrument were unplugged at this point, it would revert back to the
original displayed value upon restarting. Place the Model 2002 back in the RUN mode to store all
of the current calibration coefficients in permanent memory.
To perform a full calibration on the Model 2002 system use the Zero Coefficient Adjustment
Procedure. Follow it with the Midrange Coefficient Adjustment Procedure and after that perform
the Atmosphere Coefficient Adjustment Procedure.