69
10 Supplement
WIKA Operating Instructions - Process pressure transmitter CPT-2x
Time pe-
riod
Measuring cell ø 28 mm
Measuring cell ø 17.5 mm
All measuring ranges Measuring range
0 … +0.025 bar
(0 … +2.5 kPa)
All process fittings
Process fitting G½
(ISO 228-1)
One year
< 0.05 % x TD
< 0.1 % x TD
< 0.1 % x TD
< 0.25 % x TD
Five years < 0.1 % x TD
< 0.2 % x TD
< 0.2 % x TD
< 0.5 % x TD
Ten years < 0.2 % x TD
< 0.4 % x TD
< 0.4 % x TD
< 1 % x TD
Tab. 25: Determination of the long-term stability from the table, consideration for one year: F
stab
= 0.05 % x TD
4. Calculation of the total deviation - digital signal outputs
1. step: Basic deviation F
perf
F
perf
= √((F
T
)
2
+ (F
Kl
)
2
)
F
T
= 0.79 %
F
Kl
= 0.2 %
F
perf
= √(0.79 %)
2
+ (0.2 %)
2
)
F
perf
= 0.81 %
2. step: Total deviation F
total
F
total
= F
perf
+ F
stab
F
perf
= 0.81 % (result of step 1)
F
stab
= (0.05 % x TD)
F
stab
= (0.05 % x 2.5)
F
stab
= 0.125 %
F
total
= 0.81 % + 0.125 % = 0.94 %
The total deviation of the measurement is hence 0.94 %.
Deviation in bar: 0.94 % of 4 bar = 0.038 bar
The example shows that the measurement error in practice can be considerably higher than the
basic deviation. Reasons are temperature influence and Turn down.
