Hawassa University
School of Postgraduate Studies
Department of Chemistry
Chemical Instrumentation (Chem. 572)
Review Exercises
1) Discuss how each of the following transducers are used in chemical instruments
Photomultipliers (Phototransducer)
Charge-transfer transducers
Thermocouples
Pyroelectric transducers
2) What is a data domain?
3) What is a transfer function of the transducer?
4) Give examples of analog and time domain signals
5. The circuit that follows is for a laboratory potentiometer for measuring unknown voltages Vx.
Assume the resistor AB is a slide wire whose resistance is directly proportional to its length.
With the standard Weston cell (1.018 V) in the circuit a null point was observed when contact C
was moved to a position 84.3 cm from point A. When the Weston cell was replaced with a cell of
an unknown voltage Vx, a null was observed at 44.3 cm. Find the value of Vx.
6. What are the ideal characteristics of OP AMPs?
7. Draw the symbol of OP AMP?
8. Using appropriate circuit elements and symbols draw circuit diagram for each of the following
and suggest their applications in chemical instruments.
a) Voltage divider
b) Current divider
c) The inverting amplifier
d) The noninverting amplifier
e) The voltage follower
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f) The current follower
g) The summing amplifier
h) The difference amplifier
i) The cascaded amplifier
9. Figure below shows an operational difference amplifier measuring the output voltage of a pair
of thermocouples. Show that the output voltage (Vo) is given by:
𝑅
𝑉𝑜 = 𝑘 (𝑉2 − 𝑉1 )
𝑅𝑙
10. By means of a derivation, show that the output voltage Vo, and the input voltage Vi for the
following circuit are related by
𝑅1 + 𝑅2
𝑉𝑜 = (
)𝑉𝑖
𝑅1
11. For the circuit shown below find an expression for the output voltage.
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12. Find an expression for the output voltage in in terms of the resistance and input voltages for
the differential amplifier shown in below.
13. Assume the op amps are ideal, find the voltage gain (v0/ vi) of the following circuits.
14. Design an inverting amplifier with a gain of -15.
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15. Design a noninverting amplifier with a gain of 10
16. Design an op amp circuit to perform the following operation:
Vo = 3V1-2V2
All resistances must be  100 k
17. Design a difference amplifier to have a gain of 2 and a common mode input resistance of 10
k at each input.
18. Design a circuit having an output given by
−𝑉𝑜 = 3𝑉1 + 5𝑉2 − 6𝑉3
19. Design a circuit to perform the following calculation:
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−𝑉𝑜 = 10(5𝑉1 + 3𝑉2
20. What types of noise are frequency dependent? Frequency independent?
21. Name the type or types of noise that can be reduced by
(a) decreasing the temperature of a measurement.
(b) decreasing the frequency used for the measurement.
(c) decreasing the bandwidth of the measurement.
22. Suggest a frequency range that is well suited for noise minimization. Explain.
23. Why is shielding vital in the design of glass electrodes that have an internal resistance of 106
Ohms or more?
24.
Source:
1) Douglas A. Skoog et al. 6th Ed. 2007. Principles of Instrumental Analysis
2) Electronic material, Chapter 5. Operational Amplifiers
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