Electrical Measurement 4

Electrical measurements

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Q1. Calibration and configuration of electronic test equipment

Calibration involves applying known and accurately determined input to ensure that a specific output is indicated. 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. 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

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

I considered a digital multimeter for calibration:

Here are the Minimum-Use-Specifications that can produce an accuracy of at least ¼ of the Instrument Under Test- thermometer, hydrometer, test leads, capacitance and continuity Test Fixture, diode text fixture and a Rotek Model 2500 Calibrator. Procedure:

Q2. Evaluation of own test measurements related to limitations of the test equipment.

  1. Switch the equipment to the ON state, for 5 minutes. Perform the tests with ambient temperature of 250C±2C at a below 72% relative humidity.
  2. Change or remove the IUT’s (instrument under test) battery and then clean the battery contacts.
  3. Connect common terminals and the V/ohm channel too to the calibrator with and check the counter-check the values against the standard charts, to check for resistance.
  4. Adjust the settings for readings to be for continuity. Let the V/ohm and the common terminals be connected to the test leads. The continuity test fixture of 200Ω test points should fit the test.
  5. Set the calibrator setting to 0V input. Then connect the V/ohm and common channel to the calibrator.
  6. Choose the voltage range of IUT from the standards and set the calibrator output to the corresponding IUT input voltage. The tests done under this section form the DC Voltage test.
  7. For an AC Voltage Test, the calibrated is set to approximately 50Hz. In some countries, the standard voltage is 60hz. Connect with the calibrator the common input and V/ohm terminals. The IUT common can be connected with the ground or common of the calibrator. Select a suitable voltage range is selected in the IUT and then a good IUT input voltage to the calibrator. This has to be conducted within acceptable errors limits of voltage.
  8. The next testing sector in the AC Current test, the calibrator output is set to 0mA. The calibrator output is connected to the common terminal of the UIT V/ohm and to the terminal for low current input. The low input current is set to a typical figure of 100mA. The multimeter shall not be exceeded the maximum current rating. Failure to adhere to this will spoil the equipment. choose a correct range of current from the standard tables and charts, the calibrator output set in order to give the IUT input current correspondent.
  9. The Logic test is the last activity. It function shows whether the equipment is indicating the correct state. To do this, insert the test leads into the V/ohms and the common terminals to set the IUT. Short the leads together to determine whether the meter shows a low logic gate. Verify that the meter indicates a low logic state by setting the calibrator to 0.100VDC
  10. Try to increase the voltage setting at the calibrator to 3.500VDC then check whether the IUT is in high logic state of operation. (Patel, Huang, Piemonte & Mayor, 2013)

The calibrated equipment must meet the set standards for it to be reliable. Reliability is the dependability and consistency a test measure has. The measures that are claimed to be measured by the test equipment must be truly measured in a consistent and reliable manner. The accuracy of my test equipment is affected by the psychological state of the test taker. Excitement, stress 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 noise from nearby signals, temperature, and lightning.

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

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. (Jin, Choi, Lee, & Yang, 2008, April)

Q3. Importance of resolution, accuracy, sensitivity bandwidth and input impedance on test equipment performance.

Any machine must have clearly defined characteristics like resolution, sensitivity, accuracy, tolerance, precision, error, repeatability, reproducibility and range. These are meant to help the ones using the instrument to known the safe error operation limits.

Resolution of an electrical equipment is defined as the smallest change in the measurand or the input variable that is just sufficient to cause a change noticeable at the output display of the equipment. resolution differentiates two close and nearly equal input values.

Accuracy of an instrument is the closeness of measurements made to the absolute value. The absolute value used for comparison is an agreed standard value which is the best estimate from the many lab tests done at the industries.

Accuracy: a = ± |value measured- absolute value|

A system may have multiple input given accuracy limits s with accuracy limits of its many constituents like ± m1, ±m2, ±m3

Overall accuracy will be: A = ± (b1+b2+b3)

The root mean accuracy ARMS= sqrt (b12+b22+b32).

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

Test equipment sensitivity, is a ratio given by S = scale deflection/value of the measurand causing change. It is the magnitude ratio of the system’s output signal : the input. For example, when designing weighing machine like though found on weigh bridges, the pressure of the weight of the vehicles is transformed into some other parameter like resistance. An ammeter reading with a specific voltage supply will give the weight of the vehicle in the form of resistance.

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. Higher frequencies than these are hard to measure.

For any test equipment, the input impedance needs to be very high, not less than ten times the source impedance. When this impedance is small, the electronic circuitry of the system becomes overburdened with loading. To illustrate this, here’s an example:

If we have a 12V signal with a 5kΩ source impedance. Connecting with 1MΩ input impedance, the input voltage becomes: 12V*1MΩ/ (1MΩ + 5KΩ) = 11.94V

Should the input impedance be 8kΩ, input voltage becomes: 12V*8kΩ/ (5kΩ + 8kΩ) = 7.38V. as much as we need to have a very high impedance, when it exceeds a certain limit, the amount of power transferred becomes small. The input impedance should not be infinitely big, since the power transferred will be less when the figure goes up so high. (Plouffe et al., 2014).

Q4. Benefits and limitations of programmable controller for a specific application

Programmable controllers are known as the PLCs, widely used in all manufacturing processes in industries. They are approximately 60years old since their inception in 1958. They can perform very complex functions like communication, data sequencing, counting, timing and logic flows, doing control functions like switching industrial machines and manufacturing processes, and data execution. The technology is universally used due to its ability to withstand adverse weather conditions- which could be too cold or too hot to the point of destroying or tampering with the control equipment. The advantages of the controllers are majorly in their memory capacity and the flexibility of the hardware parts. They are highly reliable in many environments due to 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. (ZHANG, MA & LIU, 2014)

By nature, the PLCs are very small. They need a small physical space to install them. 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. With proper installation that is done in a clear and comprehensive manner, the afterward maintenance team finds troubleshooting process very easy. The circuitries are wired in a simple manner that one line of circuit command can be disconnected in case problems arises. In industries where it is unacceptable to have the production process stop due to the millions of profits which will go to waste, the ability of comfortably disconnecting one line of command of operation ensures production is a never-stopping activity.

PLCS can be used in environments where the conditions are very hash like huge vibrations that can wreck an ordinary system with instability. The PLC technology is very useful in mining industries, they can stand high humidity, noise and huge fluctuations in temperature. The programming languages required are very easy in coding control programs.

PLCs have very many input/output ports for the large scale ICs. Some have as many as 12,000 inputs. A variety of devices can be manned without any need of customizing different controls separately. The beauty of such a structure is that a wide variety of input and output interfaces can be seemly connected and towards to the output. (da Silva, Kaminski & Gruber, 2014). 

Demerits of programmable controller are far few as compared to the strengths, and majorly technical. Some of the circuits can be very big to analyse to a new personnel. It may be suppressing experience to a new personnel doing maintenance for huge circuits. The production process may be jeopardized if a very competent person will not be sourced early enough. It will necessitate a very highly skilled work force to trouble shoot the whole circuit and fix the problem as soon as possible.

Q5. Calibration procedure for an electronic test equipment.

The electronic torque wrench calibration is the instrument under consideration. This equipment is designed to allow accurate manual tightening of fasteners that have been threaded. The areas of application of the technology include operating controls digital displays, the audible alarms, control electronics and others. A sample procedure to calibrate the test equipment will be:

References

  1. Remove the end from the handle of the IUT, then turn on the Torque Tester and allow a 15min period for warming up before any results can be read from it.
  2. Mount the IUT to the Torque Tester, and using a cable provided, the wrench is connected to the Platter Interface. Next, you will need to fix one cable end to the wrench handle receptacle, and the second end be connected to the platter interface receptacle.
  3. 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. When all has been set, turn on the meter and immediately set the voltage ranger to 3V. This is to expose the adjusting knobs, angular, torque etc. after removing 2 screws and the plastic cover.
  4. 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. 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.
  5. 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. (Åström & Wittenmark, 2013)
  6. Åström, K. J., & Wittenmark, B. (2013). Computer-controlled systems: theory and design. Courier Corporation.

    da Silva, G. C., Kaminski, P. C., & Gruber, G. E. (2014). Usage of Digital Factory in the Analysis of Automotive Production Scenarios: Available Software and Resources (No. 2014-36-0329). SAE Technical Paper.

    Jin, S. M., Choi, J. J., Lee, D. Y., & Yang, S. Y. (2008, April). Development of remote control system for field robot. In Smart Manufacturing Application, 2008. ICSMA 2008. International Conference on (pp. 428-432). IEEE.

    Patel, P., Huang, R. K., Piemonte, P. S., & Mayor, R. (2013). U.S. Patent No. 8,370,097. Washington, DC: U.S. Patent and Trademark Office.

    Peterson, M. Instrumentation & Control Experimental Analyses.

    Plouffe, J., Davis, S. H., Vasilevsky, A. D., Thomas III, B. J., Noyes, S. S., & Hazel, T. (2014). U.S. Patent No. 8,776,050. Washington, DC: U.S. Patent and Trademark Office.

    ZHANG, H., MA, Y., & LIU, K. (2014). Real-time Audio and Video Data Acquisition andCompression System Based on LabWindows/CVI. Video Engineering5, 056.