MKS UniMag 971, Operation And Installation Manual, Page: 31 / 44

971 UniMag ™ Operation manual 28
Applications
Q:
Can the transducer and sensor element continuously withstand vibrations from a mechanical fore-pump.
A: Yes – the cold cathode sensor can withstand continuous vibrations.
Q:
When the transducer is pumped down and isolated by closing a valve the pressure is raising. Is the
transducer leaking?
A: Not likely - when a confined space is evacuated and the pumping is stopped the pressure will rise
because of out gassing, mainly by water vapor. The pressure can easily rise to a few Torr over time.
Q: When the transducer is leak checked on a helium leak detector, leak reading is building up slowly after
approximately 30 seconds. Is the transducer leaking?
A: No - the internal sealing of the 971 transducer uses elastomer viton sealing and consequently helium
molecules can penetrate though the viton material and cause slow increase of helium leak readout. If a
leaking transducer is tested directly on a helium leak detector the leak is almost instant displayed.
Q: Can the transducer be mounted in any orientation?
A: Yes - the transducer can be mounted in any orientation without compromise of performance or calibration.
However it is recommended not to mount the transducer with the flange port facing upwards to avoid
contamination like particulates or liquids from entering the device.
Q: Can the transducer withstand instant ventilation?
A: Yes – However, it’s not recommended to perform instant ventilation when the Cold Cathode is turn on.
Q: Can I connect a valve to be controlled by the transducer relay contact?
A: Driving inductive loads such as valves requires special precautions. Refer to detailed description page 12.
Q: How many pressure cycles can the transducer withstand?
A: Cold Cathode sensor element is very mechanical robust to pressure changes and there are no limits on
the number of pressure cycles. In applications where fast pressure cycles occur, the Cold Cathode sensor
can be sputtered and this can lead to change of accuracy.
Q: The Cold Cathode sensor chamber has changed color, Why?
A: If the Cold Cathode is operated at high pressure (>1.00E-4 Torr) the cold cathode sensor module can be
sputtered. This will change the color of the internal measuring chamber and can also result in change of
measuring accuracy.
Analog output
Q:
What is the update rate of the analog output?
A: 16 times per 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 cable length up
to 100 m do not normally require any special precautions other than the cable must be screened.
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.
Digital output
Q:
How fast can I request pressure measurements via the digital interface?
A: 10 times per second is the fastest recommended pressure request frequency.
Q: How long is the waiting time from turning power on to valid measuring values?
A: The power on sequence is approximately 2 seconds. The LED is illuminating red during power up
sequence and the digital interface will not reply to commands. The ionization can take a few minutes to
stabilize. It the cold cathode is turned on at low pressure <1.00E-7 Torr it can take several minutes before
the ionization starts.