HELP 21

Question

Answer 1

(5.1)

Properties of an ideal operational amplifier:

• Infinite input impedance.

• Zero output impedance.

• Zero common-mode gain, or, infinite common-mode rejection.

• Infinite open-loop gain.

• Infinite bandwidth.

• Infinite power supply rejection ratio.

Answer 2

(6.1)

Differences between SCR and TRAIC:

SCR:

1.SCR is a unidirectional device.

2.The gate current can be only positive.

3.SCR can operate in only one quadrent of v-i characteristics.

4.UJT is used for triggering SCR.

TRIAC:

1.TRIAC is a bi-directional device.

2.Gate current can be positive or negative.

3.It can operate in two quadrants of v-i characteristics.

4.Diac is used for triggering triac.

Answer 3

(5.3)

Step 1:

The capacitance of a integrator amplifier is .

The input resistance is .

The input volatage is .

The rate of change of output voltage is .

.

.

Solution:

The rate of change of Output volatage is .

Answer 4

(5.5)

Comparator amplifier:

Comparator is a device which compares two voltages or currents, and switches its output to indicate which is larger.

It has two analog input terminals and and one binary digital output .

The output is ideally .

Answer 5

(6.2)

SCR:

A silicon controlled rectifier is a semiconductor device that acts as a true electronic switch.

It can change alternating current into direct current and at the same time can control the amount of power fed to the load.

Thus SCR combines the features of a rectifier and a transistor.

LASCR:

Light activated SCR (LASCR) or a Photo SCR  is just an ordinary SCR except that it can also be light triggered.

Most LASCRs also have a gate terminal for being triggered by an elec­trical pulse just as a conventional SCR.

As the name suggests, its state is con-trolled by the light falling on depletion layers.

In a normal SCR, gate current turns on the device. In the LASCR, instead of having the external gate current applied, light shinning on the device turns it ON.

Just as a normal SCR, the LASCR will continue to conduct even if the light source is removed.

The LASCRs find many applications including optical light controls, relays, phase control, motor control and a large number of computer applications.

So, LASCR can be used in a circuit to replace an SCR.

Answer 6

(6.3)

Circuit of an LASCR by transistors

Answer 7

(6.4)

Construction of TRAIC:

Triac is a semiconductor device of three terminals that is used to control the average current flow to a load, with the particularitity of which it leads in both senses and it can be blocked by investment of the tension or when falling the current below the value of maintenance.

1. Triacs are bidirectional devices.

2. Triac is designed to conduct load current in either direction.

Answer 8

(6.5)

Quadracs are a special type of thyristor which combines a diac and a traic in a single package.

The diac is the triggering device for the triac.

Therefore, the statement is true.

Answer 9

(7.1)

In practice, strain measurements rarely involve quantities larger than a few millistrain.

Therefore, to measure the strain requires accurate measurement of very small changes in resistance.

For example, suppose a test specimen undergoes a strain of 500 me.

A strain gage with a gage factor of 2 will exhibit a change in electrical resistance of only 2 (500 x 10^-6) = 0.1%.

For a 120 Ω gage, this is a change of only 0.12 Ω.

To measure such small changes in resistance, strain gages are almost always used in a bridge configuration with a voltage excitation source.

The general Wheatstone bridge, illustrated in Figure , consists of four resistive arms with an excitation voltage, V_EX, that is applied across the bridge.

Answer 10

(7.2)

The general Wheatstone bridge, illustrated in Figure , consists of four resistive arms with an excitation voltage, V_EX, that is applied across the bridge.

From this schematic, it is apparent that when R₁R₃ = R₂R₄, the voltage output V₀ is zero.

Under these conditions, the bridge is said to be balanced, and any change in resistance in any arm of the bridge results in a non-zero output voltage.

Therefore, if you replace R₄ with an active strain gauge, any changes in the gauge’s resistance will unbalance the bridge and produce a non-zero output voltage.

It is then possible to create an algorithm in the data acquisition software to convert this output into a unit of force.

The basic principle is expressed in the following equation :