OZONE ANALYZER BMT 964 Manual, Rev. 04/2021
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non-volatile memory will only tolerate a limited (1,000,000) number of write cycles. Reading
commands can be used infinitely.
A detailed description of Link-Mode commands can be found in Appendix A.
8 Zeroing the BMT 964
The zero reading of the instrument (the value displayed without any ozone in the cuvette) may
undergo slight changes, which among others can be induced by
namely: soiling of the cuvette
aging of the UV-lamp
influence of temperature
In order to compensate these effects BMT MESSTECHNIK recommends zeroing the BMT 964
every 24 hours. Depending on the demands on accuracy and individual stability of an instrument
the time interval between two zeroing actions can be much longer.
It is very important to really make sure that no ozone is present in the cuvette during ze-
roing! Before zeroing the BMT 964 has to be purged with oxygen or filtered air.
Zeroing can be initiated in the following ways:
pressing the ZERO button with succeeding confirmation
driving the Zero-input (Pin 11) with 24 VDC
via the serial interface in User-Mode by sending the character 'A'
automatically, time controlled by the BMT 964 internal timer (see page 23)
via the serial interface in Link-Mode by sending the command *83#3.14159
from a Windows-PC by using the program BMT 964 Link
The display will show information about zeroing. In each zero cycle the dirtyness of the cuvette
is determined. This value is displayed on the front panel and sent via the serial interface. In-
creased dirtyness will lead to a Dirty Warning or a Dirty Error respectively (see page 26).
During the whole zeroing action the last measured concentration result is used to set the analog
outputs to a constant value. The serial interface in User-Mode sends out the last measured con-
centration and, instead of dirtyness, the string 'AAAA'.
Automatic Zeroing with Control of Purge Gas
Purge gas control can be taken over by the BMT 964. The relay contact Purge (Pin 2) is used for
this purpose. This contact (max. 28V, 0.5A) can switch e.g. a BMT Purge Unit PUDC2, which
consists of a solenoid valve and a small air pump with dust filter. An external 24 VDC power
supply is necessary to power the PUDC2. Alternatively, the instrument can be ordered with a
built-in Internal Purge Unit. In both cases the parameter Autozero Interval has to be set to a
time interval between 1 hour and 99 hours (either by use of the front panel menu, the program
BMT 964 Link or the Link-Mode command *45#). Automatic zeroing will be activated after this
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