LEYBOLD THERMOVAC TTR 101 N, Operating Manual, Page: 33 / 42

33 300544655_002_C1 - 11/2016 - © Leybold
FAQ (Frequently Asked Questions)
Applications
Q:
Can the transmitter and sensor element continuously withstand vibrations from a mechanical fore-pump?
A: Yes
– the MEMS Pirani sensor element can withstand continuous vibrations.
Q:
When the transmitter is pumped down and isolated by closing a valve the pressure is raising. 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 by water vapor. The pressure can easily rise to a few mbar over time.
Q: When the transmitter is leak checked on a helium leak detector. Leak reading is building up slowly after
approximately 30 seconds. Is the transmitter leaking?
A:
No - the internal sealing of the TTR 101 N THERMOVAC transmitter uses elastomer FPM sealing and
consequently helium molecules can permeate e through the FPM material and cause slow increase of helium leak
readout. If a leaking transmitter is tested directly on a helium leak detector the leak is almost instantly displayed.
Q: Can the transmitter be mounted in any orientation?
A: Yes - the transmitter can be mounted in any orientation without compromise of performance or calibration.
However it is recommended not to mount the transmitter with the flange port facing upwards to avoid contamination
like particulates or liquids from entering the device.
Q: Can the transmitter withstand instant ventilation?
A: Yes - the MEMS Pirani and Piezo sensor elements are extremely robust to mechanical forces and can withstand
continuous pressure cycles and instant air ventilation.
Q: Can I connect a valve to be controlled by the transmitter relay contact?
A: Driving inductive loads such as valves requires special precautions. Refer to detailed description in chapter 4.2.
Q: How many pressure cycles can the transmitter withstand?
A: Both the MEMS Pirani and Piezo sensor elements are very robust to pressure changes and the number of
pressure cycles will have no effect on the lifetime of the transmitter. The sensor element is very robust to pressure
changes and the number of pressure cycles will have no effect on the lifetime of the transmitter. The setpoint relay
contact endurance is minimum 2,000,000 cycles at 30VDC/0.2A load.
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. Cable lengths 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 light ring is illuminating red during power up sequence
and the digital interface will not reply on commands. Reliable measurements are typically available within 1 minute.
Q: The first character is sometimes lost in the transmitter digital communication reply?
A: This can be caused by too fast transmitter communication reply. See RS delay command description in the
Communication Protocol 300544663 (RS232).