FT651-059
9
8
Adjusting the Crystal Gauge Unit
By adjusting the crystal gauge, measurements of greater accuracy can be obtained. Adjust
the zero point and ATM as follows.
（1）
Zero Adjustment
If foreign material becomes stuck to the sensor, the high vacuum pressure reading may drift
higher. In this situation, operate the zero point set switch to adjust the zero point.
Procedure:
①
Pump down the inside of the vacuum vessel and check the pressure is at 10
-2
Pa or
below.
If the zero point drifts greatly due to insufficient base pressure, the
pressure reading will also drift greatly.
②
Press the zero set switch on the controller for 1 second or longer. Or, input an ON
signal for 1 second or longer by operating from the remote I/O.
The pressure range in which the zero point can be set is where the drift
is within approximately 10 Pa compared to when the sensor was new. If
this range is exceeded, a zero set error will occur. If the gauge is
operating at the correct pressure, the sensor has expired and needs
replacing. See Section 7 for the method of replacing the sensor.
③
Automatic Zero Adjustment
In addition to operation
②
written above, the zero can be adjusted automatically in
conjunction with the B-A gauge.
When the B-A gauge is ON, if the B-A measurement pressure remains below the
zero reset allowing pressure (1.33 x 10
-2
Pa), the zero point is automatically adjusted
every 5 minutes.
（2）
ATM Adjustment
When the gauge head has been replaced, if the pressure reading is different compared to
other gauges, adjust the ATM pressure.
When adjusting the ATM pressure, also adjust the zero point again.
Procedure:
①
Attach a standard vacuum gauge that can measure atmospheric pressure (ionization
vacuum gauge, etc.) to the vacuum vessel together with the crystal gauge.
②
Pump down the inside of the vacuum vessel and then introduce N
2
gas into the
vacuum vessel until the pressure is at atmospheric pressure.
③
Turn the ATM volume control and adjust the pressure signal output until the
pressure reading is the same as the one of the standard vacuum gauge.
④
When the ATM pressure has been adjusted by method
③
above and is to be
re-adjusted to the same pressure, it can be set by the remote control input.
