delabs Circuits

Monday, February 16, 2009

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.

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.

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)

Circuits by Application

Analog Circuits

  1. Battery Level Indicator
  2. Simple Sample and Hold
  3. Sample and Hold Standby
  4. Voltmeter Attenuator
  5. Precision Current Source
  6. Opamp Supply Virtual Ground

SCR and Triac

  1. Solid State Relay
  2. Normally Closed AC SSR
  3. AC-AC-SSR
  4. DC-DC SSR
  5. 2N2646 based Pulser
  6. Drive SCR thyristor

Mains Power

  1. Flashing Neon Lamp
  2. Dimmer power control
  3. Edison Bulb Life Extend
  4. Mains Current LED
  5. Mains Voltage LED

Digital Circuits

  1. Simple Digital Counter
  2. Running Lights
  3. Frequency Divider
  4. Crystal Oscillator
  5. Simple High speed switch
  6. Differential TTL converter

Measureall DMM

  1. Ohmmeter Measure Resistance
  2. Precision Digital Attenuator
  3. Precision Amplifier

Mixed Circuits

  1. Monostable Multivibrator
  2. Digital to Analog
  3. LM311 Oscillator
  4. PLL using 4046
  5. VCO with LM331
  6. BCD Thumbwheel to Analog
  7. V to F Converter ICL8038
555 Circuits
  1. OR gate with two 555
  2. fixed frequency duty cycle
  3. Pulse width modulation
  4. Astable Multivibrator
  5. uC Reset Generator
  6. LM555 Voltage Doubler
  7. 555 Power Oscillator
Discrete Circuits
  1. Isolated dual supply
  2. Sound to light converter
  3. Water operated relay
  4. Telephone Indicator
  5. Passive volume control
  6. RS232 Opto-Isolation
  7. Voltage Level Indicator
  8. Relay Driver
  9. Constant Current LED
  10. Voltage Doubler
  11. FET Current Source
Opamp Circuits
  1. Three Opamp Differential
  2. Two Opamp Differential
  3. Buffer Opamps
  4. Differential Op-Amp
  5. Inverting Opamp
  6. Non Inverting Opamp
  7. Digital gain control
  8. Square Triangle Oscillator
  9. Dual Polarity Output Amps
  10. Ammeter Precision Rectifier
  11. Voltage / Current 4-20 mA
  12. Current Source for RTD
Power Electronics
  1. Dual Power Supply
  2. Single Power Supply
  3. Battery Backup Supply
  4. 5V 1A Supply LM2575
  5. 5V Power Supply L296
  6. Dual Power Supply
  7. Tubelight Electronic Choke
  8. Voltage Doublers Multipliers
  9. White LED Lamp on Ni-Cd

uC and uP

  1. PC RS232 with MAX232A
  2. Battery Backup SRAM
  3. watchdog uC uP systems
Instrumentation Circuits
  1. Mains monitor LM3914
  2. Simple Mains monitor
  3. single digit voltmeter
  4. High Resistance Meter
  5. Diode Thermometer
  6. Function Generator
  7. Diode Leakage Tester
  8. Analog LED Ohm Meter
  9. Millivolt Source Current Loop
Process Control
  1. AD590 - temperature
  2. Thermocouple Amplifier
  3. Linearizing Thermocouple
  4. Thermocouple Amplifier
  5. 0-1V to 4-20 mA
  6. 1-5V to 4-20 mA
  7. InfraRed - Optical Switch
  8. InfraRed Detector