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300544660_002_C1
11/2016
- © Leybold
7
FAQ (Frequently Asked Questions)
Applications
Q:
Can the transmitter be used with corrosive gases?
A:
Yes, the transmitter uses nickel alloys exclusively in its sensor, and thus can operate in corrosive environments,
but users should expect drift and frequent zeroing in such applications.
Q:
When the transmitter is pumped down and isolated by closing a valve, the pressure is rising. Is the transmitter
leaking?
A:
Not likely. When a confined space is evacuated and the pumping is stopped the pressure will rise because of
outgassing, mainly from water vapor desorbing from the chamber walls. The pressure can easily rise to a few Torr
over time.
Q:
When the transmitter is leak-checked on a helium leak detector, the leak reading rises slowly after
approximately 30 seconds. Is the transmitter leaking?
A:
No. The transmitter
’s sensor is fully welded and has no
leak path to atmospheric pressure. However, seals in
the vacuum system typically use elastomers such as Viton
®
, and consequently helium molecules can penetrate
though the Viton and cause a slow increase of helium leak readout. If a leaking transmitter is tested directly on a
helium leak detector, the leak will be displayed almost instantly.
Q:
Can the transmitter be mounted in any orientation?
A:
The transmitter can be mounted either vertically or horizontally. Transmitters with ranges lower than 1 Torr will
experience a span shift due to the effects of gravity on the sensor diaphragm if they are mounted horizontally.
These transmitters would also see a degraded accuracy value.
Q:
Can the transmitter withstand instant ventilation?
A:
Yes. The sensor element is extremely robust to mechanical forces and can withstand continuous pressure
cycles and instant venting to atmospheric pressure. However, depending on the temperature of the ventilation, a
shift in the transmitter’s output may occur due to ei
ther heating or cooling effects from the airflow.
Q:
Can the transmitter withstand mechanical vibrations?
A:
Yes, but only for short periods of time. The transmitter will not suffer damage from short-term exposure to
mechanical vibrations, but depending on the frequency of the vibrations, there may be some variations in the
output signal due to resonance of the diaphragm.
Q:
How many atmospheric pressure cycles can the transmitter withstand?
A:
The sensor element has been tested to more than 5 million atmosphere-vacuum cycles without damage.
Analog output
Q:
What is the update rate of the analog output?
A:
For transmitters with ranges > 1 Torr (1.33 mbar), the analog output signal is updated approximately 1000/sec.
For transmitters with ranges
≤
1 Torr (1.33 mbar), the analog output signal is updated approximately 500
times/second.
Q:
What is the maximum length of analog output cable?
A:
The length of analog cable depends on cable quality and electrical noise environment, but a cable length up to
50 m (164 ft) does normally not require any special precautions other than the cable must be shielded.
Q:
The digital reading is correct, but the analog output reading has some deviation from actual pressure.
A:
Check that the analog out is connected to a floating input and not an input that is connected to ground. If
connected analog out return is connected to ground the supply current will flow in the signal line and cause voltage
drop and ground looping.
