AD549 Analog Devices, AD549 Datasheet - Page 17

• Manufacturer Part Number: AD549
• Description: Ultralow Input-Bias Current Operational Amplifier
• Manufacturer: Analog Devices

Specifications of AD549

• -3db Bandwidth: 1MHz
• Slew Rate: 3V/µs
• Vos: 500µV
• Ib: 150fA
• # Opamps Per Pkg: 1
• Input Noise (nv/rthz): 35nV/rtHz
• Vcc-vee: 10V to 36V
• Isy Per Amplifier: 700µA
• Packages: TO-X

The pH probe output is ideally 0 V at a pH of 7, independent
of temperature. The slope of the transfer function of the probe,
though predictable, is temperature dependent (−54.2 mV/pH at
0°C and −74.04 mV/pH at 100°C). By using an
ture sensor and an
compensation network can be added to the basic pH probe ampli-
fier. Table 4 shows voltages at various points, thereby illustrating
Table 4. Illustration of Temperature Compensation
Probe Temperature (°C)
0
25
37
60
100
AD534
STEEL PROBE
IN STAINLESS
analog divider, an accurate temperature
OR AC2626
AD590
OUTPUT
+
–
PROBE
A (Probe Output) (mV)
54.20
59.16
61.54
66.10
74.04
pH
(A)
AD590
Figure 46. Temperature Compensated pH Amplifier
1kΩ
12kΩ
tempera-
3
2
AD549
8
SCALE FACTOR
Rev. H | Page 17 of 20
7
4
ADJUST
0.1µF
0.1µF
1kΩ
B (A × 13.51) (V)
0.732
0.799
0.831
0.893
1.000
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 (AD590 Output) (V)
7.32
7.99
8.31
8.93
10.00
14
8
0.1µF
0.1µF
OUT
Y
Y
2
1
12
7
6
(D)
OUTPUT
D (10 × (B ÷ C)) (V)
1.00
1.00
1.00
1.00
1.00
AD549