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11 Supplement
Additional deviation through electromag-
netic interference acc. to EN 61326
Specifications apply also to the current output
Temperature drift - Current output
Deviation on the current output through
analogue/digital conversion
Deviation on the current output due to
strong, high frequency electromagnetic
fields acc. to EN 61326
Influence of the superimposed gas and pressure to the accuracy
The propagation speed of the radar impulses in gas or vapour above the medium is reduced by
high pressure. This effect depends on the superimposed gas or vapour and is especially large at
low temperatures.
The following table shows the resulting deviation for some typical gases and vapours. The specified
values refer to the distance. Positive values mean that the measured distance is too large, negative
values that the measured distance is too small.
Gas phase
Temperature
Air
20 °C/68 °F
200 °C/392 °F -0.01 %
400 °C/752 °F -0.02 %
Hydrogen
20 °C/68 °F
200 °C/392 °F -0.02 %
400 °C/752 °F -0.02 %
Steam (satu-
100 °C/212 °F 0.26 %
rated steam)
180 °C/356 °F 0.17 %
264 °C/507 °F 0.12 %
366 °C/691 °F 0.07 %
Characteristics and performance data
Measuring frequency
Measuring cycle time
Ʋ Standard electronics approx.
Ʋ Electronics with increased sensitivity
approx.
Step response time
2)
Beam angle
3)
Ʋ Clamp 2", 3"
Time span after a sudden measuring distance change by max. 0.5 m in liquid applications, max 2 m with bulk
2)
solids applications, until the output signal has taken for the first time 90 % of the final value (IEC 61298-2).
Outside the specified beam angle, the energy of the radar signal is reduced by 50 % (-3 dB)
3)
56
< ±50 mm
±0.03 %/10 K relating to the 16 mA span max. ±0.3 %
< ±15 µA
< ±150 µA
1 bar
10 bar
(14.5 psig)
(145 psig)
0.00 %
0.22 %
0.13 %
0.08 %
-0.01 %
0.10 %
0.05 %
0.03 %
-
2.1 %
1.44 %
1.01 %
K-band (26 GHz technology)
450 ms
700 ms
≤ 3 s
18°
LEVEL TRANSMITTER 8138 • 4 ... 20 mA/HART - two-wire
Pressure
50 bar
100 bar
(725 psig)
(1450 psig)
1.2 %
2.4 %
0.74 %
1.5 %
0.52 %
1.1 %
0.61 %
1.2 %
0.37 %
0.76 %
0.25 %
0.53 %
-
-
-
-
9.2 %
-
5.7 %
13.2 %
200 bar
(2900 psig)
4.9 %
3.0 %
2.1 %
2.5 %
1.6 %
1.1 %
-
-
-
76 %
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