Digital Capacitance Meter

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Discipline: Digital measuring parameters of the components and circuits

Subject: Digital Capacitance Meter

Year: 2009

Setting: unknown capacitor capacitance Cx is measured with a digital meter two-terminal transit-time parameters such as:

1) Draw a block diagram of such a device and illustrate its operation by means of three time diagrams drawn below each other in the same scale:
- Voltage on the exemplary (measured) capacitor;
- The voltage at the output of comparator (comparator, the zero-body);
- Pulse sequence, which is input to the counter.

2) Figure out how to look digital display instrument and fix it his testimony, t. E. The value of the measured capacitance, if the number of pulses counted counter is N. Be sure to specify a unit of the measured physical quantity and to fix the decimal point in the corresponding discharge digital indicator.

3) Determine the value of the absolute quantization error (discrete) of such a device, ie. E. The unit price of LSB its indicator. What is the error - systematic or random? Is it possible to exclude from the measurement result by making a corresponding amendment? Take, if possible. If you can not, explain why. Please rate the relative measurement error due to quantization operation.

4) Determine the absolute measurement error due to the fact that the trigger level comparator (comparator, zero-body) is not equal to the desired value. Drinking Ux / U0 equal 0,6321 × U0. Explain the occurrence of this error on the corresponding timeline. What it will be error - random or systematic? Is it necessary to take into account its sign? Is it possible to assess the true value of the measured capacitance, making a corresponding amendment? If you can, do it; if you can not, explain why.

5) Identify how absolute and relative errors should set the frequency reference (crystal) oscillator device f0 ± f and the value of a model of resistance Robr ± R, that these errors did not affect the accuracy of measurement, ie, the corresponding changes to the readings would be an order of magnitude less than the error of discontinuity (quantization). Record in accordance with the rules of the desired frequency and resistance in the form: f0 ± f Robr ± R and using the required number of significant digits.

6) Record the final estimate of the true value of the measured capacitance Cx with the correct for systematic error in the form Sdeystv ± C (where C is the resulting random measurement error) with the required number of significant digits.

Initial data:

- Robr k = 0.1;
- Fobr = 0.1 MHz;
- N = 5513;
- UX / U0 = 0,62