The measurement sensor includes

1. Primary Sensors
2. Variable conversion elements
3. Signal processing
4. Signal recording

Primary Sensors:- The first element in any measuring system is the primary sensor: this gives an output that is a function of the measurand (the input applied to it). Some examples of primary sensors are a liquid-in-glass thermometer, a thermocouple, and a strain gauge. In the case of the mercury-in-glass thermometer, the output reading is given in terms of the level of the mercury, and so this particular primary sensor is also a complete measurement system in itself. However, in general, the primary sensor is only part of a measurement system. 

Variable conversion elements:- Variable conversion elements are components that transform the electrical signal from the sensors into a form that can be easily processed and analyzed by other components in the system. This may involve amplification, filtering, or other types of signal conditioning. Signal processing elements are components that analyze and interpret the electrical signal from the sensors and conversion elements, typically using algorithms and software to extract useful information from the raw data. This may involve tasks such as filtering, noise reduction, feature extraction, or pattern recognition.

Signal processing elements:- Signal processing elements exist to improve the quality of the output of a measurement system in some way. It is important that the measurement system is designed properly such that the output from measurement sensors is of appropriate amplitude and is as free from noise contamination as possible.

A measuring system typically consists of all three components: sensors, variable conversion elements, and signal processing elements.

Sensors are devices that detect and measure physical quantities such as temperature, pressure, or humidity, and convert them into an electrical signal that can be processed by other components in the system.

Secondary instruments are devices used to measure electrical quantities such as current or voltage, and they can only determine the value of the quantity being measured if the instrument has been calibrated beforehand.

Calibration is typically done by comparing the instrument with either an absolute instrument, which is highly accurate and precise or a calibrated instrument. The calibration is necessary to ensure the accuracy and reliability of the measurement taken by the secondary instrument.

There are three types of secondary instruments: indicating instruments, recording instruments, and integrating instruments.

Indicating instruments provide a reading of the magnitude of the quantity being measured through the use of a dial and pointer.

Recording instruments, on the other hand, provide a continuous record of the quantity being measured over a specified period. They use a pen attached to the moving system of the instrument to record variations in the quantity being measured on a sheet of paper that moves perpendicular to the pen's movement.

Integrating instruments are used to record totalized events over a specified period of time. They calculate the product of time and an electrical quantity, which provides the summation of the events being measured. Examples of integrating instruments include ampere-hour and watt-hour meters, which are used to measure the amount of electrical energy consumed over a period of time.

In general, secondary instruments are widely used in most applications, whereas absolute instruments are typically only used in standard laboratories or similar institutions.

• A pointer of an instrument once deflected returns to zero position, when the current is removed due to Controlling Torque.
• When an electrical instrument is used to measure a quantity, such as current or voltage, the instrument's moving system is deflected from its original position.
• The deflection is caused by the deflecting torque, which is proportional to the quantity being measured.
• The instrument's moving system is then maintained at the new position by a controlling torque, which opposes the deflecting torque.
• When the current is removed, the deflecting torque is eliminated, and the controlling torque becomes the only torque acting on the instrument's moving system.
• The controlling torque is designed to be such that it causes the moving system to return to its original or zero position, thus resetting the instrument for the next measurement.

• In hot wire instrument, the sensing wire is made of Platinum-iridium.
• Platinum-iridium is a common material used for sensing wire in hot wire instruments.
• Platinum-iridium alloys have a high melting point, good mechanical strength, and are relatively resistant to oxidation at high temperatures, making them suitable for use in hot wire instruments.

• An ammeter is inserted in Series in a circuit and current to be measured flows through it.
• An ammeter is an instrument used to measure the electrical current in a circuit.
• It is connected in series with the circuit, which means that the current to be measured flows through the ammeter.
• The ammeter typically has a low resistance, so it does not significantly affect the current being measured.
• By connecting the ammeter in series, the current to be measured passes through the instrument and creates a magnetic field that causes a deflection of the ammeter's moving system.
• The extent of the deflection is proportional to the magnitude of the current, and the ammeter is calibrated to provide a direct reading of the current being measured.

• An ammeter is convertible to a voltmeter by Putting a large resistance in series with the actual measuring part of the instrument.
• It is possible to use an ammeter as a voltmeter by connecting a high-value resistor in series with the ammeter.
• The resistor limits the current flowing through the ammeter, which allows it to be used as a voltmeter by measuring the voltage drop across the resistor.
• This is known as the voltmeter multiplier technique, and it allows the ammeter to be used to measure voltage up to its maximum voltage rating.

• Manganin is preferred as a shunt for extending the range of measurement of a voltmeter.
• Manganin is a type of resistance wire that is often used as a shunt for extending the range of measurement of a voltmeter.
• Manganin has a very low-temperature coefficient of resistance, which means that its resistance does not change significantly with temperature.
• This makes it an ideal material for shunts, as it ensures that the shunt's resistance remains stable over a wide temperature range.
• When a shunt is connected in parallel with a voltmeter, it diverts a known fraction of the current around the voltmeter, allowing the voltmeter to measure the remaining voltage drop across the load.
• The shunt's resistance is carefully chosen so that the voltage drop across it is proportional to the current flowing through it, which allows the current to be accurately calculated from the voltmeter reading.
• "Manganin is preferred as a shunt for extending the range of measurement of a voltmeter, due to its low-temperature coefficient of resistance and stability over a wide temperature range."

• The size of the slide wire of the potentiometer to make it achieve high accuracy should be as long as possible.
• The accuracy of a potentiometer depends on several factors, including the quality of the materials used, the precision of the manufacturing process, and the method of measurement.
• However, the size of the slide wire can also play a role in determining the accuracy of the potentiometer.
• A longer slide wire allows for finer adjustments and reduces errors due to wire resistance and contact resistance.
• This is because a longer wire has a greater resistance, which reduces the impact of contact resistance and wire resistance on the measurement.
• Additionally, a longer wire allows for more precise positioning of the sliding contact, which can improve the accuracy of the measurement.
• However, there are practical limitations to the length of the slide wire, such as cost, space constraints, and the need for a higher driving voltage to achieve the same level of sensitivity.
• Therefore, the size of the slide wire should be carefully chosen to balance the need for accuracy with practical considerations.

To convert the galvanometer into an ammeter, a shunt resistor is connected in parallel with the galvanometer. The resistance of the shunt is given as 75 ohms and the internal resistance of the galvanometer is given as 25 ohms.

Let the current flowing through the shunt resistor be I_s and the current flowing through the galvanometer be I_g.

According to Kirchhoff's current law, the total current in the circuit is equal to the sum of the currents flowing through the shunt and the galvanometer.

Therefore, I_s + I_g = 5 A .....(1)

The potential difference across the galvanometer is given by Ohm's law as follows:

V_g = I_g * R_g = I_g * 25

The potential difference across the shunt resistor is also given by Ohm's law as follows:

V_s = I_s * R_s = I_s * 75

Since the shunt and the galvanometer are connected in parallel, the potential difference across both of them must be the same. Therefore:

V_g = V_s

Substituting the values of V_g and V_s, we get:

I_g * 25 = I_s * 75

Solving for I_s, we get:

I_s = (1/3) * I_g

Substituting this value of I_s in equation (1), we get:

(1/3) * I_g + I_g = 5

Simplifying, we get:

I_g = 3.75 A

Therefore, the current flowing through the galvanometer is 3.75 A.

• Voltmeter is not an integrating instrument.
• An integrating instrument is one that records the totalized events over a specified period of time.
• These instruments are used to measure the total amount of a physical quantity that has accumulated over a period of time. Examples of integrating instruments include ampere-hour meters and watt-hour meters.
• An ampere-hour meter is an integrating instrument used to measure the total amount of electrical charge that has been consumed in a circuit over a specified period of time.
• It works by integrating the product of time and the current flowing through the circuit. The resulting value is measured in ampere-hours, which represents the total amount of charge that has been consumed.
• Similarly, a watt-hour meter is an integrating instrument used to measure the total amount of electrical energy that has been consumed in a circuit over a specified period of time.
• It integrates the product of time and the power (voltage multiplied by current) consumed by the circuit. The resulting value is measured in watt-hours, which represents the total amount of energy that has been consumed.
• On the other hand, a voltmeter is an instrument used to measure the voltage difference between two points in a circuit.
• It is not an integrating instrument as it only measures the instantaneous value of the voltage at a particular moment in time. It does not record the total amount of voltage that has accumulated over a period of time.