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| 型号： | AB-151 |
| 英文描述： | AB-151 - FOUR-WIRE RTD CURRENT-LOOP TRANSMITTER: Four-Wire Connections to an RTD Allow the RTD to be Remotely Located from Active Circuitry. Yet Maintain Accuracy |
| 中文描述： | 抗体- 151 -四线RTD电流环变送器：四线连接到一个RTD的电阻允许被远程位于从有源电路。然而，保持准确度 |
| 文件页数： | 5/5页 |
| 文件大小： | 78K |
| 代理商： | AB-151 |
5
density of the resistor’s current noise) into Equation 2
results in
The integral in Equation 4 can be shown to equal 1/(2T
INT
)
so that after taking the square root, Equation 4 reduces to
giving the root-mean-square (rms) value of the noise. To
express the noise in “ppm of full scale”, divide Equation 5
by the integrator’s full-scale voltage, V
FS
=V
REF
= Q
FS
/C
INT
,
through the math shows that the resulting transfer function is
The normalized AC portion of Equation 3 is shown in Figure
11. The units of the transfer function are V/A since the
DDC112 integrates a current to produce a voltage.
Substituting Equation 3 and S()
= S
i
()
=
4KT/R (spectral
and multiply by 10
6
. The result, the rms thermal noise of the
resistor seen at the DDC112’s output in units of ppm of full-
scale, is
Combining the resistor noise with the “internal” noise of the
DDC112 gives the total noise seen at the output. The internal
noise is the noise produced by the DDC112 without the
resistor. It is proportional to the sensor capacitance and
inversely proportional to the DDC112’s full-scale range.
The DDC112 data sheet provides typical “rms ppm of full
scale” values in the Typical Performance Curves section.
Since the two noise sources are independent, they add as
“powers” and the total noise equals
Figure 12 shows the results of actual noise measurements vs
the calculated noise of Equation 7. The Evaluation Fixture
was configured as shown in Figure 7 to measure the noise
with different values of T
INT
, Q
FS
, and R as shown.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
FIGURE 11. Normalized Frequency Response of the
DDC112’s Front End Integrators for T
INT
=
500
μ
s.
FIGURE 12. Measured and Calculated Noise vs R for
Different Values of T
INT
and Q
FS
.
100
1k
1/T
INT
10k
100k
0
–10
–20
–30
–40
–50
I
Frequency (Hz)
H() =
sin(
π
T
INT
)
π
T
INT
(3)
H
T
C
T
T
INT
INT
INT
INT
( )
=
(
)
sin
π
π
(4)
v
KT
R
T
C
T
T
d
INT
2
INT
INT
INT
2
2
0
2
4
=
∫
(
)
∞
sin
π
π
(5)
v
C
KT
R
T
INT
INT
=
1
2
100
10
1
N
1
10
100
1000
RINPUT (M
)
Q
FS
= 50pC
T
INT
= 500
μ
s
Q
FS
= 50pC
T
INT
= 5000
μ
s
Measured
Data
Calculated
Curve
Q
FS
= 350pC
T
INT
= 5000
μ
s
Q
FS
= 350pC
T
INT
= 500
μ
s
References
1. Van der Ziel, Aldert;
Noise in Solid State Devices and
Circuits
; John Wiley & Sons; 1986
(6)
Noise
v
V
KT
R
Q
T
RESISTOR
FS
INT
FS
=
=
10
10
2
6
6
(7)
Noise
Noise
Noise
TOTAL
RESISTOR
DDC
=
+
2
112
2
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