Electrical Measurement

Electrical Measurement

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Q1. Importance of resolution, accuracy, sensitivity bandwidth and input impedance on test equipment performance.

All machines designed must have well defined characteristics, and this falls under the instrumentation of systems. When operation errors are defined by the functionalities of the equipment, empirical data collected will be used with understanding of error limits.

By definition, resolution of any electrical equipment refers to the smallest change in the measurand or the input variable that is just sufficient to cause a recognizable change in the output (display of the equipment). It puts a line of demarcation between two close and nearly equal input values.

Accuracy of an instrument is the closeness of measurements done to the true value that should be obtained on the measurand at hand. The absolute vale used for comparison is an agreed standard value which is the best estimate from the many lab tests done at the industries.

Accuracy is given by: a = ± |value measured- absolute value/accepted standard|

A system could be having accuracy limits of its many constituents like ± m1, ±m2, ±m3

Overall accuracy will be: A = ± (m1+m2+m3)

And the root mean accuracy ARMS= sqrt (m12+m22+m32).

Overall accuracy for the test equipment is given as a percentage of the entire equipment range. It is important in defining the maximum allowable deviation of the outcome of the instrument from the absolute value.

Test equipment sensitivity, S = scale deflection/value of the measurand causing change. It defines the magnitude ratio of the system’s output signal to the of the input. E.g., a transducer using temperature as the input variable with resistance as the output parameter will have its sensitivity as the gradient of the graph drawn of resistance against temperature. Sensitivity bandwidth is the frequency range specification with which measures can accurately be taken. The bandwidth shows the frequency at which a signal reduces to a -3Bb point. Should frequency increase to a very high figure, the test instrument wont accurately respond to the test parameters.

Input impedance for any test equipment needs to be very high, more than ten times the source impedance. Should this impedance be small, the electronic circuitry of the system or rather the equipment is overburdened with significant loading.

Say we have a 10V signal with a 2kΩ source impedance. Connecting with 5MΩ input impedance, the input voltage becomes: 10V. 5MΩ/ (5MΩ + 2KΩ) = 9.9996V

Should the input impedance be 5kΩ, input voltage becomes: 10V. 5kΩ/ (5kΩ + 2kΩ) = 7.143V. The input impedance should not be infinitely big, since the power transferred will be less when the figure goes up so high.

Q2. Benefits and limitations of programmable controller for a specific application

Programmable controllers are universally used in industries in a way to replace the relay logic, which is essentially a mechanically operated electrical circuits. They are very robust in performing functions like data sequencing, communication, doing control functions like switching industrial machines and manufacturing processes, counting, timing and logic flows, and data execution. The technology is loved by many industries because of the ability it has to withstand adverse weather conditions- which could be very cold or too hot to the point of destroying or freezing ordination control equipment. the advantages of the controllers rise from their memory capacity and the flexibility of the hardware parts. The solid-state component of a programmable controller makes it highly reliable. The memory of these controllers is programmable. Changes can be made any time to adjust some outputs. Controlling systems becomes flexible. (Baresi, Mauri, Monti, & Pezze, 2000).

The physical nature of PLCs makes them very small. They are favourable with the small spaces in. this is favourable to the manufacturers who will use the floor space more effectively than the archaic methods of doing things. The modular Input/ Output produces a neat appearance on the control panels. When the wires are neatly positioned, installation procession becomes short, with an easy maintenance done periodically. Whenever a problem arises, troubleshooting is done with the help of diagnostic indicators in a very easy manner. The manner in which they are wired is simple that one line of circuit command can be disconnect in cases of problems for repairs. The production process moves on with disrupting any kind of services.

They are rugged and designed for harsh environments. Mechanical tremors and vibrations don’t affect their functionality. In mining industries, programmable controllers are the best for implementation since the environments are full of humidity, noise and huge fluctuations in temperature. The programming languages needed to code control programs in the controllers are relatively easy to learn.

The controllers are large scale ICs which in practice have had very many input/output ports. For very complex projects, you can get a controller with 10000 inputs. The beauty of such a structure is that a wide variety of input and output interfaces can be seemly connected and towards to the outputs, a variety of devices can be manned without any need of customizing different controls separately.

The disadvantages of programmable controller are majorly technical challenges. Some of the circuits can be very big to analyse to a new personnel. At the set of a faulty, it may take a very long time to locate the source of the problem. It will necessitate a very highly skilled work force to trouble shoot the whole circuit and fix the problem as soon as possible. The production process may be jeopardized if a very competent person will not be sourced early enough.

Q3. Calibration and configuration of electronic test equipment

Calibration is the application of known and accurately determined input to ensure that a specific output is indicated. Equipment that have been in use with time cease to be accurate and there is need to periodically calibrate them to ensure that accuracy is in shaped. Errors made during measurements need to be of acceptable limits for inspection to be reliable. The process of calibration is thorough and needs to be accurate. It can either be done by an Accredited Calibration Laboratory or a Non-Accredited Calibration Laboratory using the Acceptable procedure for Equipment of Testing. (Corwith, 2000). 

What is termed as acceptable procedure is that one that has been published from the manufacturer of the test equipment. It will be necessary to calibrate an instrument just after purchase before it starts operation unless a certificate of calibration has been issued out. Also, when accuracy is in doubt or after a repair to the equipment and the periodic testing needed.

I will consider a digital multimeter (DMM) for calibration:

Here are the Minimum-Use-Specifications that can produce an accuracy of at least 1/5 of the Instrument Under Test- thermometer, hydrometer, test leads, capacitance and continuity Test Fixture, diode text fixture and a Rotek Model 2500 Calibrator. Procedure:

Q4. Evaluation of own test measurements related to limitations of the test equipment.

  1. Turn on the power for 6 minutes. Perform the tests with ambient temperature of 300C±4C at relative humidity of below 75%.
  2. Remove the IUT’s (instrument under test) battery and clean the battery contacts.
  3. Verify the functionality of the selector switch after turning on the IUT.
  4. Connect common terminals to the calibrator with the V/ohm channel too and check the counter-check the values against the standard charts, for resistance check.
  5. On the IUT, change to continuity. Let the V/ohm and the common terminals be connected to the test leads. The continuity test fixture of 100Ω test points should fit the test, for continuity check.
  6. Put the calibrator setting to 0V input. Then connect the V/ohm and common channel to the calibrator.
  7. Using the standard charts, choose the voltage range of IUT and set the calibrator output to the IUT input voltage correspondingly. This is the DC Voltage test.
  8. To conduct an AC Voltage Test, the calibrated is set to approximately 60Hz. The common input and V/ohm terminals are connected with the calibrator. The IUT common is connected with the ground or common of the calibrator. A good voltage range is selected in the IUT and then a corresponding IUT input voltage to the calibrator settled on. Limits must be checked to be within the standards set from the standard charts.
  9. For an AC Current test, the calibrator output is set to 0mA. The common terminal of the UIT is connected to the calibrator output and to the terminal for low current input. The low input current is set to a typical figure of 200mA. The multimeter shall not be exceeded the maximum current rating. Else, the equipment might be rendered useless and a scrap. With the standard tables and charts, the IUT range of current is chosen and the calibrator output set in order to give the IUT input current correspondent.
  10. The last part is the Logic test. This function shows whether the equipment is indicating the correct state. Insert the test leads into the V/ohms and the common terminals to set the IUT into the test mode. To determine whether the meter shows a low logic gate, short the leads together. Verify that the meter indicates a low logic state by setting the calibrator to 0.500VDC
  11. Increasing the voltage setting at the calibrator to 3.400VDC then check whether the IUT is in high logic state of operation. (Larson, Tong & Rajsuman, 2004). 

For a test to be considered good and reliable, it should meet some basic standards. The measures that are claimed to be measured by the test equipment must be truly measured in a consistent and reliable manner. Reliability itself is the dependability and consistency a test measure has. The accuracy of my test equipment is affected by the psychological state of the test taker. Anxiety or motivation will have an effect on the results arrived at during the time of testing. My test equipment will also be affected by the environmental factors like temperature, electrical noise and even lightning.

The form of test either parallel or alternate. They therefore can be having different data, but the measurement characteristics are similar. The test validity is a measurement characteristic showing how well the test measures were. Whereas validity tells of how the test process was good, the reliability of the test equipment is the trustworthiness. (Rodriguez-Lujan et al., 2014).

Some of the possible emerging fault conditions are as a result of vibrational stress and connectivity elements; corrosion. With time, the functionality of these equipment starts going down. The problems that come with test equipment are known. The most likely problem that can so badly rock this test equipment is the intermittent operation. This however is no major impediment to the results, since the chances of the testing devices making reading of the intermittently failed test point. Another lurking problem with Automatic Test Equipment is that the testing process is performed in a fast manner to lower the cycle time and shop costs.

Another problem that is likely to show up is the application of environmental a stress. There are cases in the past where test cables have been damaged or weakened during the test process. This adds another problem in some circuits. More loads may keep flowing to the circuitry which were never meant to be borne by the equipment’s supply voltage connectors, relays, switches and others are components

Q5. Calibration procedure for an electronic test equipment.

I have chosen the electronic torque wrench calibration. The instrument is designed to allow accurate manual tightening of fasteners that have been threaded. Areas of use include the audible alarms, operating controls digital displays, control electronics and many more. This is the procedure to calibrate the test equipment:

References

  1. To start with, the end cap is removed from the handle of the IUT, then turn on the Torque Tester and allow a 10min period for warming up before any results can be read from it.
  2. The Instrument Under Test is mounted to the Torque Tester, and using a cable provide, the wrench is connected to the Platter Interface.
  3. Fix one cable end to the wrench handle receptacle, the second end is connected to the platter interface receptacle.
  4. Two leads are connected to the multimeter’s input terminal and the other to the angle and torque jacks that is found on the unit of the Plotter Interface.
  5. When all has been set, turn on the meter and immediately set the voltage ranger to 3V.
  6. To expose the adjusting knobs, angular, torque etc. after removing 2 screws and the plastic cover.
  7. While still having the handle of the IUT, the reset button should be employed to reduce torque to zero. Have the readings of voltage on the multimeter after releasing the reset button. Press down the same reset button with different torque adjustments.
  8. Make effort to turn the potentiometer arm angle clockwise as much as possible. Take readings of the Torque tester and record them digitally on the IUT display.
  9. Repeat this over and over again with different variable inputs. When done, the multimeter is disconnected from the Plotter Interface and the protective cap replaced on the IUT. The adjusting knobs too are replaced and finally the IUT removed from the torque tester. (Sellathamby, Slupsky, & Moore, 2014). 
  10. Baresi, L., Mauri, M., Monti, A., & Pezze, M. (2000). PLCTools: design, formal validation, and code generation for programmable controllers. In Systems, Man, and Cybernetics, 2000 I EEE International Conference on (Vol. 4, pp. 2437-2442). IEEE.

    Corwith, A. E. (2000). U.S. Patent No. 6,037,787. Washington, DC: U.S. Patent and Trademark Office.

    Larson, D., Le, A., Tong, C. Q., & Rajsuman, R. (2004). U.S. Patent No. 6,804,620. Washington, DC: U.S. Patent and Trademark Office.

    Rodriguez-Lujan, I., Fonollosa, J., Vergara, A., Homer, M., & Huerta, R. (2014). On the calibration of sensor arrays for pattern recognition using the minimal number of experiments. Chemometrics and Intelligent Laboratory Systems130, 123-134.

    Sellathamby, C. V., Slupsky, S., & Moore, B. (2014). U.S. Patent No. 8,829,934. Washington, DC: U.S. Patent and Trademark Office.