937B Controller Instruction Manual
pg. 32
9. Enable
There are three
‘ENABLE’ settings available for a relay:
a. SET: forces the relay to stay in the activated (closed) state regardless of pressure and set
point values
b. CLEAR: forces the relay to stay in the deactivated (open) state regardless of pressure and
set point values.
c. ENABLE: the relay status is determined by the pressure, set point value, and direction.
10. DIR
DIR determines when the relay is activated. If ABOVE is selected, the relay will be activated
when the pressure is above (greater than) the set point. If BELOW is selected, the relay will be
activated when the pressure is below (less than) the set point. The default setting for DIR is
BELOW.
See Figure 8-1 and Section 8.2 for a more detailed description of the DIR setting.
11. SET SP
Displays the entered and saved set point trip value. To change the value, scroll to the value to be
changed, highlight by pressing ENTER, and then adjust to the desired value with the UP or
DOWN arrow keys. Confirm the change by pressing ENTER. The range is 1% to 95% of the
manometer’s full scale. When entering the value, the speed of the value change can be increased
by continuously pressing the UP or DOWN arrow keys.
12. Hyst
When a set point value is changed, the hysteresis value will be changed automatically. If DIR is
set to ABOVE, the hysteresis is automatically set to 0.9xSet point; if DIR is set to BELOW, the
hysteresis is automatically set to 1.1xSet point.
To modify the hysteresis, move the cursor to the hysteresis value and press ENTER. Use the UP
or DOWN arrow keys to change the value, then press ENTER again to set the value. When DIR
has been set to ABOVE, the maximum hysteresis value permitted for a Capacitance Manometer
is 0.99xSet point; when DIR is set to BELOW, the minimum hysteresis value is 1.01xSet point.
6.5.3
Setup for a CP (Convection Pirani), Convectron, or PR Sensor
Do not use Convection Pirani or Convectron gauges above 1000 Torr true pressure.
Series 937B Controllers are furnished calibrated for N
2
. They also measure the pressure
of air correctly within the accuracy of the instrument. Do not attempt to use a Convection
Pirani or Convectron gauge calibrated for N
2
to measure or control the pressure of other
gases such as argon or CO
2
, unless the gas type setting or accurate conversion data for
N
2
to the other gas is properly used. If accurate conversion data is not used or
improperly used, a potential overpressure explosion hazard can be created under certain
conditions.
For example, at 760 Torr of argon gas pressure, the indicated pressure on a Convection
Pirani or Convectron gauge calibrated for N
2
is 24 Torr. At an indicated pressure of 50
Torr, the true pressure of argon is considerably above atmospheric pressure. If the
indicated pressure is not accurately converted to true pressure, it is possible to
overpressure the vacuum system. Overpressure may cause glass components to shatter