1. Operational Amplifiers (Op Amps) in Chemical Instrumentation
Chapter 3:
Operational Amplifiers (Op Amps)
in Chemical Instrumentation
Look at Fig. 5-4

2. Operational Amplifiers

3. Operational Amplifiers
Functions
1. Precise measurement of voltage, current, and resistance 2. Mathematical operations - addition or subtraction - multiplication or division - integration - differentiation 3. Constant current and constant voltage sources

4. General Characteristics
Operational Amplifiers
General Characteristics
A: large open-loop gain (104 ~106) Zi: high input impedance (very high: Zi ≥ 106 ~1013 Ω) Zo: low output impedance (very small: Zo :1 ~ 10-3 Ω) zero output voltage for zero input

5. Inverting & noninverting input
Operational Amplifiers
8-pin commercial op amp.
Inverting & noninverting input
- Either input may be connected to positive or negative signals - Negative voltage to the inverting input  positive output voltage (positive voltage to the inverting input  negative output voltage) - AC signal to inverting input: 180o out of phase

6. General Characteristics
Operational Amplifiers
General Characteristics

7. Inverter/scaler (inverting amplifier)
Operational Amplifiers: feedback circuits
Inverter/scaler (inverting amplifier)
Ri = Rf  inverter
Rf > Ri  Signal amplification
(inverting amplifier)

8. Operational Amplifiers Circuits
Voltage Follower
- output voltage = input voltage
- Supply large current as the output of the operational amplifier:
it can accept an input from a device that can not supply much current
(such as glass electrode) and offer the same voltage to a significant load (e.g. recorder)

9. Voltage (Potential) Measurement
Operational Amplifiers Circuits
Voltage (Potential) Measurement -
Inverting amplifier
offer a very high input impedance
allows the measurement of a voltage without perturbing the voltage significantly

10. Operational Amplifiers Circuits
Current Measurement
Current-voltage converter (current follower)
Large Rf small current can be measured.
Rf =100kΩ, i = 1 μA
Vo = 0.1 V
(easily detected)

11. Addition or Subtraction
Operational Amplifiers Circuits
Addition or Subtraction -

12. Operational Amplifiers Circuits
Differentiation

13. Operational Amplifiers Circuits
Integration