MKS Granville-Phillips 358 series, Instruction Manual

Page: 71 / 122

Preparing for Operation
Series 358 Micro-Ion Controller Instruction Manual - 358013 - Rev. B
71
Op
er
ation
C
a
p
a
cita
nce Ma
nom
eter
Servic
e
Pre
p
a
ring
fo
r
Op
er
atio
n
5.5 Preparing for Convectron
Gauge Operation
Convectron Gauge pressures are indicated on lines A and B of the
Controller display.
Install suitable devices that will limit the pressure to the level that the
vacuum system can safely withstand. In addition, install suitable pressure
relief valves or rupture disks that will release pressure at a level
considerably below that pressure which the system can safely withstand.
Suppliers of pressure relief valves and pressure relief disks are listed in the
Thomas Register under “Valves, Relief”, and “Discs, Rupture.”
Confirm that these safety devices are properly installed before installing the
product. In addition, check that (1) the proper gas cylinders are installed, (2)
gas cylinder valve positions are correct on manual systems, and (3) the
automation is correct on automated systems.
Vacuum gauges with compression fittings may be forcefully ejected if the
vacuum system is pressurized.
5.6 Gases other than Nitrogen
or Air
Convectron Gauges are thermal conductivity gauges of the Pirani type.
These gauges transduce gas pressure by measuring the heat loss from a
heated sensor wire maintained at constant temperature. For different gases,
the heat loss is different at any given true pressure and thus the pressure
indication can be very different.
It is important to understand that the indicated pressure of a Convectron
gauge depends on the type of gas, the orientation of the gauge axis, and on
the gas density in the gauge. Convectron gauges are normally supplied
calibrated for N
2
(air has approximately the same calibration). With proper
precautions, the Convectron gauge may be used to measure pressure of
certain other gases.
The following information in this section applies only when the Convectron
Gauge has been calibrated for N
2
and when the Convectron Gauge is
mounted with its axis horizontal.
At pressures below a few Torr, there is no danger in measuring pressure of
gases other than N
2
and air, merely inaccurate indications. A danger arises
if the N
2
calibration is used without correction to measure higher pressures
of some other gases. For example, N
2
or air at 24 Torr causes the same heat
WARNING
Failure to use accurate pressure conversion data for N
2
or air to other gases can cause an explosion due to
overpressurization.
If the controller will measure any gas other than N
2
or air,
before connecting the controller to system control devices,
adjust pressure outputs for the process gas that will be used.