CN-0267 Datasheet, PDF (7/8 Pages) Analog Devices – Complete 4 mA to 20 mA Loop Powered Field Instrument with HART Interface

Circuit Note
The performance summary can be seen in Table 3, and the
signal plots are shown in Figure 8 and Figure 9.
Table 3. Primary Sensor Input Noise and Resolution
Parameter
Pressure
Sensor
Resistive
Network
Full Scale
207 kPa
246 kPa
Noise RMS
1.3 Pa
0.68 Pa
Peak-to-Peak Noise
6.8 Pa
3.6 Pa
Resolution Effective (rms)
17.2 bit
18.5 bit
Noise-Free Resolution (p-p)
14.9 bit
16.1 bit
40
35
30
25
20
0 10 20 30 40 50 60 70 80 90 100
SAMPLE
Figure 8. Pressure Sensor Input Signal Plot
10
5
0
–5
–10
0
10 20 30 40 50 60
SAMPLE
70 80 90 100
Figure 9. Resistive Network as Primary Input Signal Plot
CN-0267
Secondary Sensor Input Performance
Similar to the primary sensor, the performance of the secondary
sensor input is mainly determined by the analog front-end of
the ADuCM360 with the exception of noise performance.
The analog input was configured to transmit temperature in
degrees Celsius (°C) to a master over the HART communication
path. Analysis was performed on two tests of 100 samples to
quantify the performance.
The first test was performed using the platinum 100 Ω sensor
on the board, and the second test was performed with the sensor
replaced on the board by a standard (fixed) 100 Ω ± 1% resistor.
The performance summary is shown in Table 4, and the signal
plots are shown in Figure 10 and Figure 11.
Table 4. Secondary Sensor Input Noise Performance
Parameter
Pressure Sensor Resistive Network
Noise RMS
0.037°C
0.033°C
Noise Peak to Peak 0.19°C
0.16°C
25.0
24.5
24.0
23.5
23.0
0
10 20 30 40 50 60 70 80 90 100
SAMPLE
Figure 10. RTD (Platinum 100 Ω) Sensor Input Signal Plot
1.0
0.5
0.0
–0.5
–1.0
0
10 20 30 40 50 60 70 80 90 100
SAMPLE
Figure 11. Fixed 100 Ω ± 1% Resistor as the Secondary Input Signal Plot
Rev. A | Page 7 of 8