Search This Blog

Friday, July 27, 2018

Voltmeter Attenuator Rectifier

Measurement of Voltage : - In testing electronic circuits, Measurement of voltages is important for diagnosing faults and making the circuits work. In circuit diagrams given in equipment manuals, voltages at various points in the circuit are usually marked. A deviation from these values indicates that some component has failed and eventually leads to clues for isolating the faulty areas.

Voltage  measurement attenuator amp

Voltmeter Attenuator Rectifier

Specifications :-

D.C. Voltage
Ranges : +/- 200 mV, 2V, 20V, 200V, 2000V.
Input impedance: 10 mega ohms.
Circuit protection: + 2000V D.C. all ranges.
Over range: 100% to 1999.
Accuracy: +/- 0.5%.
A.C. Voltage
Note: Average responding Ranges calibrated for sine wave.
Ranges: 200 mV, 2V, 200V, 2000V
Input impedance 10 mega ohms.
Circuit protection : 750V r.m.s., all ranges.
Over range: 100% to 1999.
Description :-
As our DPM is capable of measuring only 200 mv full scale deflection, the input voltage in the case of exceeding the range needs scaling down. This is achieved by an attenuator chain.

Wednesday, July 18, 2018

Ammeter and Precision Rectifier

Studying current measurement is a prerequisite for many of the measuring techniques. The current parameter mainly specifies the power consumption in a circuit, given the value of resistance.

Current Shunt Amplifier digital control

It is found convenient to measure current rather than voltage for knowing power output and determining efficiency. It may be required to measure leakages in circuits at certain times. Hence the measurement of current constitutes a priority.

Ammeter and Precision Rectifier
Measurement of DC Current -

The circuit diagram for the measurement of current (d.c. and a.c. modes) is shown aside. For measurement of current switch SI is operated. The switch S-ad is kept in d.c. mode. This enables the current to pass through a shunt circuit consisting of resistors R26, R27, R28, R29 and R 30. The current ranges are provided in 5 decades i.e. 200 micro-amps, 2 milli-amps, 20 milli-amps, 200 milli-amps and 2 amps. An additional current range that can be read upto 20 Amps is also provided. However, for measuring this high current the green terminal provided on the meter should be used. When a current to be measured is fed to the input terminals of the instrument appropriately, a voltage proportional to the current through the shunt resistor is fed into the DPM which measures the d.c. voltage which in turn indicates the d.c. current being fed.

Test and Measurement Instruments

Measurement of AC Current -

In case of a.c. measurement, the switch S-ad is kept in a.c. mode. The a.c. current path is similar to the d.c. current path in the shunt resistor. However the voltage tapped across the shunt resistor is fed into IC2 which is a buffer. The output of IC2 is fed to IC3 through capacitors C10 and C11. This IC is an operational amplifier acting as a precision rectifier. The output of IC3 is fed to the input of the DPM for measuring the a.c. current being fed to the input terminals. It can be seen that the current measurement is similar to the voltage measurement except that the attenuator chain is replaced by the shunt resistor circuit.

(This is scanned-ocr from my earlier file, some mistakes corrected - delabs)

Friday, July 13, 2018

Multi Output Instrument Power Supply

Every electronic gadget primarily needs a D.C, power supply to energize it. It also forms the basic requirement for any constructional project. consequently there is a need to obtain multiple voltage values for cost reduction, convenience and compact arrangement for all the above applications

List Of Components For Power Supply.

1. Transformers - X1-6-0-6 (500 ma), X2-12-0-12 (500ma)
2. Semiconductors - IC6-7805, IC7-7808, IC8-7908, D1 to D10-IN4007, D11 and D12 - 12v, 1W, Zener
3. Resistors. - R1 and R2 - 100E 1/2 W CFR
4. Capacitors. - C 40v , C5 and C8 - 1000 Mfd , C1 - 2200 Mfd, C5 and C7 - 0.1 Mfd, C9 to C12 - 100Mfd
5. Miscellaneous -  F1-250ma, N1-Neon, 3-Pin Mains Chord.

Multi Output Instrument Power Supply

POWER SUPPLIES:

The required D.C. power supply is usually obtained by means of a transformer. It is also possible to have transformer­less power supplies. Though the elimination of the transformer makes the circuit compact, economical and simple, also facilitating quick assembly and built in short circuit protection, certain drawbacks creep in. These power supplies are useful only for low current applications.

Special safety precautions ? are to be followed while using them. Physical contact should be strictly avoided, since the output terminals are not isolated from A.C. mains supply.

Workbench Power Supply

This obviously necessitates the use of a transformer. By suitable modification it is possible to obtain multiple/ fractional dual voltages from a transformer. Different not-so obvious voltage values can also be obtained from the transformer by rectification circuits. The output so obtained from a transformer secondary is unregulated. For good load regulation, the internal impedance of any power supply should be as low as possible. The regulation can be improved either by resistor zener method or series regulator method.