Measurement and Instrumentation Laboratory Manual

Experiment 1 - Measurement errors and DC bridges

Part A - Measurement errors

Aim: To measure some unknown color coded resistors, identify & calculate measurement errors.

Calculations:

• Using the multi-meter reading as an exact value, what is the error from the nominal value in readings in method 1 & 2.
• Using the nominal E24 value of the resistors, what is the error in methods 1-3.
• Calculate and measure the resistance of the total series & parallel of the six color coded resistors

Discussion questions:

• What are the causes of the errors in method 1, 2 and 3
• What is the error between the calculated & measured values in method 4
• What if any errors can be attributed to temperature variations during your tests

Part B- Using DC bridge to measuring resistance

Aim: To measure resistance using a DC Wheatstone bridge.

Calculations:

• Calculate the measurement error for each resistor

Discussion questions:

• To what factors do you attribute measurement errors?
• What would be the effect if the excitation voltage for the bridge was a voltage other then 9 Volt?
• What would be the effect if the excitation voltage for the bridge was 12V AC?

Experiment 2 - AC bridges

Part A - AC bridge measuring capacitance

Aim: To measure & confirm the value of capacitance of several capacitors wired in various combinations

Calculations:

• Calculate the value of each of the colored resistors using the results obtained.
• The capacitors come from the E12 range of capacitors, choose the nominal E12 value of the color coded capacitors.
• Calculate the total capacitance Method 6 (i), (ii) & (iii)

Discussion questions:

• What are the causes errors in the bridge technique
• Derive the equation for balance for this bridge.
• In your calculations where should you "round" the values.
• What would have been the result DC excitation was used for the bridge

Part B- AC bridge measuring inductance.

Aim: To measure & confirm the capacitance of several inductors wired in various combinations using the Maxwell bridge.

Calculations:

• For each inductor calculate the value of R1 which would have given a complete balance.

Discussion questions:

• Did the fact that we did not use R1 to obtain a precise balance effect the balance that was achieved?
• Suggest and draw a simpler bridge which could be used for measuring inductance (similar to the bridge in Part A
• Give two disadvantages of such a bridge compared to the Maxwell bridge.
• What was the effect of having an excitation frequency of 1 KHz. And why?
• What would have been the limitation of using a multi-meter to measure the balance condition?

Experiment 3 - Basic transducer circuits

Part A - Measuring temperature

Aim: To confirm the operation of a circuit which may be used for measuring temperature?

Calculations:

• Obtain an approximate equation relating voltage to temperature

Discussion questions:

• Does the thermistor have a positive or negative temperature coefficient
• What errors are being encountered?
• Develop & draw the circuit of a simple bridge where the voltage will be zero at room temperature (say 25 Centigrade) and will read negative for lower temperatures & positive for higher temperatures.

Part B- Measuring light intensity

Aim: To confirm the operation of a circuit which may be used for measuring light intensity.

Discussion questions:

• Is the luminous intensity vs. thickness of attenuation layer linear or non-linear? Why?
• Is the luminous intensity vs. distance linear or non-linear. Why?
• Over what distance can the LDR function as a reflective sensor. What are the limitations?
• Develop & draw a circuit which could be used as a detector to measure the reflectivity of a material at a given distance, such that the material produces a positive voltage when it is highly reflective, a negative voltage if it is poorly reflective and 0 Volts when it is medium reflective.

Attachment:- Assignment File.rar