Process Unit 73 LF - Knick

Process Unit 73 LF
Calibration by Sampling
If the cell cannot be removed (e.g. for reasons of
sterility in biotechnical processes), the cell
constant can be determined by ”sampling”.
To do so, the Process Unit 73 LF stores the currently
measured process value.
Immediately afterwards, you take a sample from
the process. If possible, the sample value should
be measured directly on site, for example with a
Knick Series 910 Portable Conductivity Meter. The
determined value is entered in the Process Unit 73
LF which calculates the cell constant from the difference
between the process value and the sample
value.
During calibration, output current (1 and 2) and
controller output are frozen, limit contacts are disabled,
the “probe” contact is enabled (only with
option 352).
How to perform calibration by sampling
Press and to open the “Sample Cal”
submenu.
The measured sample temperature and the currently
measured value of the process medium aredisplayed
and stored.
In addition, you can see whether calibration is to
be performed with or without TC correction (for
parameter setting, see Pg. 9–17).
Press or to return to the Calibration
menu, or
press to activate measuring mode.
In measuring mode, the word ”Sample” in the upper
right corner of the display indicates that a
sample value has been stored for calibration. The
unit expects entry of the laboratory value. Until
that, it uses the old cell constant for measurement.
(If the unit is in remote status during interface operation,
the display ”Sample” is covered by ”Remote”.)
Without TC correction
Take a sample from the process and measure the
value of the sample at the temperature at which
the sample has been taken (“Sample Temp”, see
display). To do so, it may be necessary to thermostat
the sample correspondingly in the lab. Suitable
comparison meters are the portable Knick
Model 911 Cond or the Laboratory Conductivity
Meter 703. Temperature compensation must be
turned off at these meters (TC = 0 %/K).
6–10 Calibration