Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Dual Slope Integrating Type DVM”.
1. Why is dual slope method preferred over ramp techniques?
a) no noise
b) partial noise
c) average noise
d) maximum noise
Answer: a
Clarification: During the process of integration, noise is canceled out by the positive and negative ramps in the dual slope method. The input signal is integrated only for a fixed interval of time and this is the basis for the dual slope method.
2. What is the significance of the name dual slope method?
a) it has two slopes
b) it integrates the input twice
c) it uses two inputs
d) it has two outputs
Answer: b
Clarification: The input signal is integrated only for a fixed interval of time and this is the basis for the dual slope method. Reference voltage is integrated with a negative slope. Hence the method is known as dual slope integrating type DVM.
3. What is the output voltage in a dual slope integrating type DVM?
a) differential of the input
b) multiple of the input
c) integral of the input
d) zero
Answer: c
Clarification: In a dual slope integrating type DVM, the output voltage is given by the integral of the input voltage.
where, Vin is the input voltage
R1 is the series resistance
t1 is the time for which the capacitor is charged.
4. Input voltage depends on ____________
a) resistance
b) capacitance
c) current
d) time-period
Answer: d
Clarification: The input voltage in a dual slope integrating type DVM is given by the relation,
Vin = Vreft2 ⁄ t1
From the above equation it is seen that the input voltage in a dual slope integrating type DVM depends on the time periods t1 for which the capacitor is charged and t2 during which the capacitor is discharged.
5. Noise rejection is poor.
a) True
b) False
Answer: b
Clarification: In a dual slope integrating type DVM, the noise is cancelled out by the positive and negative ramps during the process of integration. As a result, the noise rejection is excellent.
6. What is the effect of the capacitor on the output?
a) no effect
b) charging effect
c) electrostatic effect
d) magnetic effect
Answer: a
Clarification: In the dual slope integrating type DVM method, the capacitor is connected through means of an electronic switch. As a result the effects due to offset voltage wherein there exists an output voltage without the application of any input are eliminated.
7. What is the effect of clock on the voltage?
a) voltage doubles with clock input
b) voltage halves with clock input
c) no effect
d) voltage becomes zero with clock input
Answer: c
Clarification: In a dual slope integrating type DVM, the value of the unknown voltage is independent of the frequency of the clock. It depends only on the number of counts read by the electronic counter.
8. What is the counter value at the beginning?
a) one
b) ten
c) three
d) zero
Answer: d
Clarification: In a dual slope integrating type DVM, the electronic counter is reset to 0 at the beginning of the measurement of voltage. Flip-flop output is also maintained at zero and is given to control logic.
9. What is the maximum count of the counter?
a) 9999
b) 0
c) 500
d) 1000
Answer: a
Clarification: In a dual slope integrating type DVM, the electronic counter reaches a maximum value of 9999 before resetting. A carry pulse is generating pulling down all the digits to zero. Flip-flop then activates the control logic.
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