Working of Electron Capture Detector

Electron capture detector:

This post provides an information about electron capture detector. We will also see the construction and working of electron capture detector.



Construction and working of electron capture detector:

The diagram shows electron capture detector used in chromatographic analysis of environmental samples. This detector operates similar to proportional counter used for X-ray measurement. In this detector, the effluent from the column is passed over a β emitter (Ni-63). An electron from β emitter causes ionization of carrier gas and production of a burst of electrons. In the absence of organic compounds, a constant standing current between a pair of electrodes results from this ionization process. However in presence of organic compounds the current decreases significantly. The response of this detector is nonlinear unless the applied potential across the detector is pulsed.

The electron capture detector is highly sensitive molecules containing electro-magnetive functional groups like halogens, peroxides, nitro groups; it is insensitive to the functional groups like amines, alcohols, and hydrocarbons. Hence it is a powerful tool in the determination of chlorinated insecticides.

Advantages of electron capture detector:

  • 1)      Electron capture detector is highly sensitive.
  • 2)      Non destructive to the sample.

Disadvantages of the electron capture detector:

  • 1)      Highly non linear response.
Electron capture detector
Electron capture detector
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Flame ionization detector

Flame ionization detector (FID):

Hi friends, today we will learn flame ionization detector and its working.


The diagram shows the flame ionization detector used in gas chromatography. It consists of a burner in which the effluent in the burner is mixed with hydrogen and air. This mixture is then ignited electrically. Most of the organic compounds when paralyzed at the temperature of H2/air flame, they produce ions and electrons which can conduct electrically through flame. A potential of few hundreds volts is applied across a burner tip and collector electrode located above the flame. The resulting current is then directed into a high impedance operational amplifier circuit for the measurement. Now as the number of ions produced in the flame is near about proportional to the number of carbon atoms, the current produced is also proportional to the carbon atoms in the sample.

Flame Ionization Detector
Flame Ionization Detector

The flame ionization detector is powerful detector for the analysis of organic samples because of insensitivity of flame ionization detector towards the functional groups like carbonyl, alcohol, halogen and amine as well as the noncombustible gases like H2O, CO2, NOx. It is particularly used for the detection of pollutants in natural water sample.

Advantages of flame ionization detector:

  • 1)      High sensitivity (10^-13 gm/sec.)
  • 2)      Large linear response range (10^7)
  • 3)      Low noise
  • 4)      Rugged and easy to use

Limitations of flame ionization detector:

1)      Destructive to the sample.

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• Thermal conductivity detectors
• Liquid Chromatograph (HPLC)
• Argon ionization detector
• Electron capture detector

Related searches: Flame ionization detector, gas chromatography, flame ionization detector how it works, flame ionization detector in gas chromatography.

Features of Intel 8085 microprocessor

Features of Intel 8085 microprocessor:

The features of Intel 8085 microprocessor are as follows:

Breadboard  Atmel AVR microprocessor project.
Breadboard Atmel AVR microprocessor project. (Photo credit: thepodger)

1)      8085 microprocessor is an 8 bit microprocessor. I.e. it can accept or provide 8 bit data simultaneously.

2)      8085 microprocessor is a single chip, NMOS device implemented with 6200 transistors.

3)      8085 microprocessor requires a single +5V DC power supply.

4)      8085 microprocessor provides on chip clock generator, therefore there is no need of external clock generator, but it requires external tuned circuit like LC, RC or crystal.

5)      8085 microprocessor requires two phase, 50% duty cycle, TTL clock. These clock signals are generated by an internal clock generator (refer following figure).

2 Phase TTL clock
2 Phase TTL clock

6)      The maximum clock frequency of 8085 microprocessor is 3MHz where as minimum clock frequency is 500 KHz.

7)      8085 provides 74 instructions with the following addressing modes:

  • register
  • direct
  • immediate
  • indirect
  • implied.

8)      The data bus is multiplexed with the address bus, hence it requires external hardware to separate data lines from address lines (this is one of the disadvantage of 8085).

9)      8085 microprocessor provides 16 address lines, therefore it can access 2^16 = 64K bytes of memory.

10)   It generates 8 bit I/O address, hence it can access 2^8 = 256 input ports and 256 output ports.

11)   It performs the following arithmetic and logical operations.

  • 8 bit, 16 bit binary addition
  • 2 digit BCD addition
  • 8 bit binary subtraction
  • logical AND, OR, EXOR
  • complement and shift operations.

12)   8085 microprocessor has five hardware interrupts: TRAP, RST 5.5, RST 6.5, RST 7.5, INTR

13)   The hardware interrupt capability of 8085 microprocessor can be increased by providing external hardware.

14)   8085 microprocessor has capability to share its bus with external bus controller (direct memory access controller); for transferring large amount of data from memory to I/O and vice versa.

15)   8085 microprocessor provides one accumulator, one flag register, 6 general purpose registers and two special purpose registers.

16)   It provides status for advanced control signals. (Advanced control signals are used in large systems).

17)   8085 microprocessor can be used to implement three chip microcomputer (8085, 8155, 8355)

18)   8085 microprocessor provides two serial I/O lines which are SOD and SID; it means, serial peripherals can be interfaced with 8085 microprocessor directly.

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Four Point Starter – best explained

Four point starter:

four point starter
four point starter

In four point starters, the hold on coil is connected directly across the supply line through a protective resistance R. when the armature touches stud no 1.the line current divides into three parts i) armature starting resistance and overload release. ii) a variable resistance and shunt field winding. Iii) Holding coil and current limiting resistance.

The basic difference between three point and four point starters is the manner in which the hold on coil is connected. The unnecessary tripping of starter can be stopped by connecting separately or parallel both magnetizing and field coil. They are connected in such a way that both should carry their individual current. Thus voltage drop in one coil will not affect the voltage in other coil.

Disadvantages of four coil starter:

The only limitation of the four point starter is that it does not provide high speed protection to the motor. If under running condition field gets opened; the field current reduces to zero. As there is some residual flux present and speed (N) is directly proportional to flux (ø) the motor will tries to run with dangerously high speed .this is called high speed action of motor. In three point starter as no volt coil is directly connected to across the supply; its current is maintained irrespective of the current through the field winding .hence it always maintain the handle in run position as long as supply is there .and thus it doesn’t protect the motor from field failure conditions which returns into high speeding of the motor.

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Three Point Starter

Three Point Starter – best explained

Three point starter:


three point starter
three point starter

figure shows the schematic diagram of a three point starter for a shunt motor. It is so called because it has three terminals L, F and A. the starter consist of starting resistance divided into several sections and connected in series with the armature. The tapping points of the starting resistance are brought out to a number of studs. The three terminal L, F and A of the starter are connected respectively to the positive line terminal, shunt field terminal and armature terminal. The other terminal of the armature and shunt field windings are connected to the negative terminal of the supply   .the no volt coil is connected in the shunt field circuit. One end of the handle is connected to the terminal L through the over load release coil. The other end of the handle moves against a spiral spring and make contact with each stud during starting operation cutting out more and more starting resistance as it passes over each stud in clockwise direction.

Working of three point starter:

1)      Initially when a DC supply is switched ON with handle in the OFF position.

2)     The handle is now moved clockwise to the first stud, the shunt field winding is directly connected across the supply while the whole starting resistance is inserted in series with the armature circuit.

3)     As the handle is gradually moved over to the final stud, the starting resistance is cut out of the armature circuit in steps. The handle is now held magnetically by the no volt release coil which is energized by shunt field current.

4)     If the supply voltage is suddenly interrupted or if the field excitation is accidently cut, the no volt release coil is demagnetized and the handle goes back to the OFF position under the pull of the spring. If no volt coil were not used, then in case of failure of supply. The handle would remain on the final stud. If then supply is restored, the motor will be directly connected across the supply, resulting in an excessive armature current.

5)     If the motor is overloaded (or any fault occurs) it will draw excessive current from the supply. This current will increase the ampere turns of the overload release coil and pull the armature, thus short circuited the no volt release coil. The no volt coil is demagnetized and the handle is pulled to the OFF position by the spring .thus the motor is automatically disconnected from the supply

Limitations of the three point starter:

Unnecessary tripping of starter if a field regulator is connected in series with the field windings for speed control operation. This combination and magnetizing coil will carry same current if more and more resistance is added in field regulator then current in magnetizing coil is unable to hold the arm in attracted position and unnecessarily the arm will be released even if there is no over loading .this is avoided in four point starter.

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four point starter