VEGA VEGABAR 21 - Manual (Page 26)

26 VEGABAR 21
Measurement with isolating systems
7 Measurement with isolating systems
Application limits
Isolating systems extend the temperature
and product application range of pressure
transmitters considerably. Therefore check in
addition that the complete measurement loop
suits the temperature. If due to the tempera-
ture conditions, a high ambient temperature
can be caused on the instrument, the use of
a cooling element or a capillary will be neces-
sary.
The max. permissible gauge pressure on the
separating diaphragm should not exceed a
value of -500 mbar. Should higher low pres-
sure values be expected, please contact us
respectively.
Error treatment
The influence of an isolating system is directly
determined by the temperature of the isolat-
ing liquid in front of the measuring cell. The
temperature coefficient Tk (see „1.5 Technical
data“) is valid for silicone oil. It reduces with
water-glycerine to 50 % of the values.
The total temperature error results in the sum
of Tk
Pressure transmitter
and Tk
Isolating diaphragm
:
Tk
tot
= Tk
Isolating diaphragm
+ Tk
Pressure transmitter
Example:
You use an isolating system with a Tk of
2,7 mbar/10 K (acc. to „1.5 Technical data“).
Your pressure transmitter has a measuring
range of 0 … 1 bar and a Tk of 0,05 %/10 K
(acc. to technical data). This corresponds to
a Tk of 0,5 mbar/10 K.
Tk
total
=
= 2,7 mbar/10 K + 0,5 mbar/10 K
= 3,2 mbar/10 K
We recommend the use of a process pres-
sure transmitter with the max. available accu-
racy level to keep the total error within the
limits.