WinSystems PCM-A/D-12, Руководство по эксплуатации

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13
®
ADS7807
used for each input range (see Figure 8). The input resistor
divider network provides inherent overvoltage protection
guaranteed to at least
±
25V.
Analog inputs above or below the expected range will yield
either positive full scale or negative full scale digital outputs
respectively. Wrapping or folding over for analog inputs
outside the nominal range will not occur.
CALIBRATION
HARDWARE CALIBRATION
To calibrate the offset and gain of the ADS7807 in hard-
ware, install the resistors shown in Figure 7a. Table VII lists
the hardware trim ranges relative to the input for each input
range.
SOFTWARE CALIBRATION
To calibrate the offset and gain in software, no external
resistors are required. However, to get the data sheet speci-
fications for offset and gain, the resistors shown in Figure 7b
are necessary. See the No Calibration section for more
OFFSET ADJUST GAIN ADJUST
INPUT RANGE RANGE (mV) RANGE (mV)
±
10V
±
15
±
60
0 to 5V
±
4
±
30
0 to 4V
±
3
±
30
TABLE VII. Offset and Gain Adjust Ranges for Hardware
Calibration (see Figure 7a).
200
Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
33.2k
Ω
100
Ω
V
IN
200
Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
100
Ω
+5V
66.5k
Ω
V
IN
200
Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
33.2k
Ω
100
Ω
V
IN
FIGURE 7b. Circuit Diagrams (Without Hardware Trim).
details on the external resistors. Refer to Table VIII for the
range of offset and gain errors with and without the external
resistors.
NO CALIBRATION
See Figure 7b for circuit connections. Note that the actual
voltage dropped across the external resistors is at least two
orders of magnitude lower than the voltage dropped across
the internal resistor divider network. This should be consid-
ered when choosing the accuracy and drift specifications of
the external resistors. In most applications, 1% metal-film
resistors will be sufficient.
±
10V 0-5V 0-4V
FIGURE 7a. Circuit Diagrams (With Hardware Trim).
200
Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
33.2k
Ω
100
Ω
V
IN
1M
Ω
+5V
50k
Ω
50k
Ω
200
Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
1M
Ω
+5V
50k
Ω
50k
Ω
33.2k
Ω
100
Ω
V
IN
200
Ω
1
2
3
4
5
6
AGND2
REF
CAP
R2
IN
AGND1
R1
IN
+
+
2.2µF
2.2µF
1M
Ω
+5V
50k
Ω
+5V
100
Ω
33.2k
Ω
50k
Ω
V
IN
±
10V 0-5V 0-4V