ad549sh-883b Analog Devices, Inc., ad549sh-883b Datasheet - Page 17

• Manufacturer Part Number: ad549sh-883b
• Description: Ultralow Input Bias Current Operational Amplifier
• Manufacturer: Analog Devices, Inc.

The pH probe output is ideally 0 V at a pH of 7, independent of
temperature. The slope of the probe’s transfer function, though
predictable, is temperature dependent (−54.2 mV/pH at 0 and
−74.04 mV/pH at 100°C). By using an
sensor and an
compensation network can be added to the basic pH probe
amplifier. Table 4 shows voltages at various points, illustrating
Table 4. Illustration of Temperature Compensation
Probe Temperature
0°C
25°C
37°C
60°C
100°C
AD534
analog divider, an accurate temperature
STEEL PROBE
IN STAINLESS
OR AC2626
AD590
OUTPUT
+
–
PROBE
AD590
A (Probe Output)
54.20 mV
59.16 mV
61.54 mV
66.10 mV
74.04 mV
pH
(A)
temperature
Figure 46. Temperature Compensated pH Amplifier
1kΩ
12kΩ
3
2
AD549
8
SCALE FACTOR
Rev. G | Page 17 of 20
7
4
ADJUST
0.1µF
0.1µF
1kΩ
B (A 3 13.51)
0.732 V
0.799 V
0.831 V
0.893 V
1.000 V
6
+15V
the compensation. The AD549 is set for a noninverting gain of
13.51. The output of the AD590 circuitry (Point C) is equal to
10 V at 100°C and decreases by 26.8 mV/°C. The output of the
AD534 analog divider (Point D) is a temperature-compensated
output voltage centered at 0 V for a pH of 7 and has a transfer
function of –1.00 V/pH unit. The output range spans from
−7.00 V (pH = 14) to +7.00 V (pH = 0).
26.6kΩ
(B)
(C)
Point
10
11
1
2
Z
Z
X
X
2
1
1
2
AD534
+15V
–15V
C (590 Output)
7.32 V
7.99 V
8.31 V
8.93 V
10.00 V
14
8
0.1µF
0.1µF
OUT
Y
Y
2
1
12
7
6
(D)
OUTPUT
D (10 B/C)
1.00 V
1.00 V
1.00 V
1.00 V
1.00 V
AD549