MKS HPS 937A Series, Руководство по эксплуатации и техническому обслуживанию владельца, Страница: 89 / 108

937A Multi-Sensor System
A.10
Preventing Contamination in a Pirani Sensor
Locate and orient a Pirani sensor to avoid contamination which might affect
the tube's element. For example, if a sensor is installed directly above a
roughing pump in the system, oil vapor could contaminate the tube's filament
wire and cause the calibration to shift.
Install a Pirani sensor with the vacuum port facing downward whenever
possible to prevent particulates and liquids falling or flowing into it. Using a
screen or porous filter at the port is helpful. Try an HPS
TM
Product seal and
centering ring assembly with a screen (see Accessories, p.67).
Series 315/345 Pirani Sensor
Orienting the Series 315/345 Pirani Sensor
Operating position has no effect on accuracy. The Pirani sensor was
designed to minimize the effects of convection. In a standard Pirani
system, the ouput of the sensor changes very little between the horizontal
and vertical position.
The Series 315/345 Pirani sensor exhibits slight convection
characteristics near atmosphere. Therefore, the best accuracy can be
achieved above 30 Torr by calibrating the sensor oriented vertically with
the port facing down. The Pirani sensor can be calibrated at any pressure
between 600 and 1000 Torr.
Connecting the Series 315/345 Sensor
To fit a KF 16 port to a KF 10 port, use an HPS adaptive centering ring
(HPS™ PN 100315821)
To install the Sensor with a
1
/8" NPT,
do not use the case for tightening. Use
the
9
/16" hex flats on the sensor’s vacuum tubing for tightening. Wrap about
two turns of Teflon
®
tape on the threads of the Sensor in the direction of the
threading to ensure a leak-free seal.
Do not use a compression mount (quick connect) to attach the
Sensor to a system in positive pressure applications.
Positive pressures might blow the Sensor out of a compression fitting,
damaging equipment and possibly injuring personnel.
A solid electrical connection between the Sensor and the
grounded vacuum system must be provided to shield the tube
element from external radiation sources.
In applications where the system may be exposed to large voltage
fluctuations, a centering ring with a screen should be installed, and the
screen and tubing then grounded. The clamp must be tightened properly so
the flange contacts the centering ring.