40 IM/261Gx/Ax-EN Rev. 08 | 261Gx, 261Ax
9.3 Measuring accuracy
9.3.1 Reference conditions according to IEC 60770
— Ambient temperature TU = constant in the range
18 ... 30 °C (64 ... 86 °F)
— Humidity r.F = constant, in the range 30 ... 80 %
— Ambient pressure PU = constant in the range
950 ... 1,060 mbar.
— Measuring span based on zero point
— Transmitter with separating diaphragm or Hastelloy
— Filling fluid: silicone oil
— Supply voltage: 24 V DC
— Load with HART: 250 Ω
— Transmitter not grounded
— Characteristic curve setting: linear, 4 ... 20 mA.
Unless otherwise stated, errors are specified as a % of the
measuring span value.
The accuracy of the measurement in relation to the upper
range limit (URL) is affected by the turndown (TD); i.e., the
ratio of the upper range limit (URL) to the set span (URL/span).
FOR OPTIMUM MEASURING ACCURACY, IT IS
RECOMMENDED THAT YOU SELECT THE SENSOR CODE
WHICH WILL PROVIDE THE LOWEST TD VALUE.
9.3.2 Dynamic response (according to IEC 61298-1)
Reaction time 100 ms
Time constant (63.2 % of total step
response)
150 ms
9.3.3 Measuring error for setting cut-off point
Turndown Measuring error
1:1 … 10:1 ±0.1 %
>10:1 ± (0.1 + 0.005 x TD - 0.05) %
9.3.4 Ambient temperature
Thermal change in ambient temperature as regards the zero
signal and span (turndown up to 6:1), in relation to the set
span
Temperature range
Maximum effect on zero signal
and span
-10 … 60 °C (14 … 140 °F) All measuring ranges
± (0.2 % x TD + 0.2 %)
-40 … -10 °C (-40 … 14 °F)
All measuring ranges
±((0.1 % / 10 K) x TD + (0.1 / 10K))
60 … 85 °C (140 … 185 °F)
9.3.5 Temperature coefficient (T
k
)
Effect of the ambient temperature per 10 K (but limited to the
maximum effect of the temperature change, see previous
information). The information refers to the set measuring span.
Temperature range Effect on zero signal and span
-10 … 60 °C (14 … 140 °F)
Sensor code C, F:
± (0.15 % x TD + 0.15 %)
Sensor code L, D, U, R, V:
± (0.05 % x TD + 0.05 %)
9.3.6 Power supply
Within the specified limits for the voltage / load, the total
influence is less than 0.001 % of the upper measuring range
limit per volt.
9.3.7 Load
Within the specified load / voltage limits, the total influence is
negligible.
9.3.8 Electromagnetic fields
Total influence is less than 0.3 % of measuring span from
80 … 1,000 MHz and for field strengths up to 10 V/m when
tested with unshielded conduit, with or without meter.
9.3.9 Mounting position
Nominal position: vertical; process connection at bottom.
Mounting position deviant from the standard position influence
the output due to the filling liquid. With a deviation of 90° from
standard position the effect is 1.12 mbar + 0.01 mbar/10K.
This effect can be compensated by carrying out zero signal
adjustment and configuring the mounting angle with the LCD
indicator or DTM.
9.3.10 Long-term stability
±(0.10 x TD) % / year
9.3.11 Vibration effect
±(0.10 x TD) % acc. to IEC 61298-3
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