Rosemount 3244MV, Справочное руководство

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Reference Manual
00809-0100-4799, Rev BA
September 2002
Model 3244MV
A-4
Table A-2. RTD Sensor Input
Approximate Basic Error
Examples of Approximate Basic Error Calculation:
Given:
• Total cable length = 150 m
• Unbalance of the lead wires @ 20 °C = 0.5
Ω
• Resistance/length (18 AWG Cu) = 0.025 Ω /m
• Temperature Coefficient (Cu) = 0.0039 Ω / Ω / °C
• Approximate Pt 100 resistance variation with temperature = 0.39 Ω / °C
Pt 100 3-wire RTD:
• Lead wire resistance seen by the transmitter = 0.5 Ω
• Basic error = 0.5 Ω /(0.39 Ω / °C) = 1.3 °C
• Error due to an ambient temperature variation of ± 25 °C = ± 0.13 °C
Pt 100 2-wire RTD:
• Lead wire resistance seen by the transmitter =
150 m 2 wires 0.025 Ω /m = 7.5 Ω
• Basic error = 7.5 Ω /(0.39 Ω /°C) = 19.2 °C
• Error due to an ambient temperature variation of ± 25 °C = ± 1.9 °C
Thermocouple and Millivolt Input
• dc input impedance > 10M ohms.
Example of Approximate Error Calculation:
RFI Effect
Worst case RFI Effect is equivalent to the transmitter’s nominal accuracy
specification per “Accuracy” on page A-3 when tested in accordance with EN
61000-4-3, 10 V/m, 80 to 1000 MHz, and 30 V/m, 26-500 MHz (Increased
NAMUR), with twisted shielded cables (Type A Profibus type).
Vibration Effect
Transmitters tested to the following specifications with no effect
on performance:
FrequencyAcceleration
10–60 Hz0.21 mm peak displacement
60–2000 Hz3 g’s
Self Calibration
The transmitter’s analog-to-digital circuitry automatically self-calibrates for
each temperature update by comparing the dynamic measurement to
extremely stable and accurate internal reference elements.
Sensor Input Approximate Basic Error
4-wire RTD None (independent of lead wire resistance)
3-wire RTD ± 1.0
Ω
in reading per ohm of unbalanced lead wire resistance
(1)
(1) Unbalanced lead wire resistance = maximum imbalance between any two leads.
2-wire RTD 1.0
Ω
in reading per ohm of lead wire resistance
Approx. Error
Total Sensor Lead Resistance
10M ohms
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 
Absolute Value of Reading in mV
×
=