Electronics Guru: April 2017

Friday, 21 April 2017

How diode works - what happens inside a diode when it comes into contact with power

Diode is a p-type and n-type materiel semiconductor device. This allow to pass the current flow in only one direction (called the diode's forward direction), while blocking current flow in the opposite direction (called the reverse direction). At this time there are many types of diodes uses in electronics designing like schottky diode, LED (light emitting diode), zener diode, photodiode, tunnel diode and many types.

Working

Small voltages to be required to operate diodes, for silicon diodes 0.6v would be need to get conduct and 0.3v required for germanium diodes.

When a battery negative connect to diode N-type (cathode) and positive connect to P-type (anode), it says "Forward-bias". In this condition depletion zone shrinks and holes flow p-type side and electrons flow n-type side, it's mean current flows.

However if we connect battery in reverse direction, it says "Reverse-bias". The result is that, depletion zone gets wider, this depletion region acts as an insulator preventing current from flowing through the diode and all of the electrons be gathered p-type end and holes at n-type end. In this condition no current flows in circuit because electrons and holes are moving in wrong direction.

So we can say diode works as a check valve that allow to water flow in one direction only.

When water pressure on left overcomes the restoring force of spring, the gate is opened and water is allowed to flow. When water pressure is from right to left, the gate is pressed against the solid stop and no water is allowed to flow. Spring restoring force is analogous to 0.6V needed to forward bias a Si diode.

Tuesday, 18 April 2017

PT1000 temperature sensor chart & calculations (C codes)

What is PT1000 type sensor?

PT1000 is a platinum resistance thermometer (PRTs). It offers to sense -200 to +850 degree centigrade with high accuracy. Various manufacturer offer to different types minimum to maximum working conditions, different error percentages.

The working procedure of pt1000 sensor is vary platinum aliment's resistance according to temperature. We can measure temperature to find the aliment resistance. Basically sensor has 1000Ω resistance at the 0°C. So we say it PT1000, other sensors like PT100 has 100Ω at 0°C.

PT1000 temperature vs resistance chart :- https://drive.google.com/file/d/0B886Kbl42IVuMmhXTTluV1NTTjg/view?usp=sharing

Temperature Calculation

Temperature is proportional to sensor resistance value with a little error percentage. We can get accurate temperature with given below linearization equation.

As PRT’s are not completely linear polynomial approximation is required. In the range -200°C ≤ ϑ < 0°C electrical resistance at temperature t is calculated according to the polynomial:

In the range of 0°C ≤ ϑ ≤ 850°C coefficient c is set to zero and the polynomial becomes:

For conversion of electrical resistance to temperature the above equations can be used after solving for t:

Polynomial coefficients for conversion of resistance to temperature, or vice versa, from platinum resistance thermometers according to IPTS-68 and ITS-90 scale.

Coefficient IPTS-68 ITS-90
a +3.90802E-03 +3.9083E-03
b -5.80195E-07 -5.7750E-07
c -4.27350E-12 -4.1830E-12

Where constants A, B, and C are derived from experimentally determined parameters α, β, and δ

using resistance measurements made at 0 °C, 100 °C and 260 °C.

The self-heating of an RTD sensor is most often expressed in mW/°C, which refers to the power required to raise the internal element temperature 1°C. Thus, the higher this figure, the lower the self-heating will be. For example, assume that 2mA of excitation current is used to drive a 100Ω platinum RTD at 100°C. This produces a sensor resistance of 138.5 Ω. Its self-heating specification is 50mW/°C in water moving at 1m/second.
It is important to note that the effective self-heating of an element depends strongly on the medium in which it is immersed. For example, an RTD can self heat 100x higher in still air than in the moving water to which this specification applied.

C codes :-

#include <math.h>

float ADC()

{

float Resistance, Add_To;

ADCON0=0x01; // Use AN0 (10 bit ADC) for sensor input

ADCON0bits.GO = TRUE;

while( ADCON0bits.GO == TRUE );

Add_To = 1024 - (ADRESL + (ADRESH * 256 ));

Add_To = 1024 / Add_To;

Resistance = 1000.0 * (Add_To - 1);

return Resistance;

}

void Calculate_Temp(float R)

{

float A = 3.9083E-3;

float B = -5.775E-7;

float T;

R = R / 1000; // We multiplied resistance with 1000 in

ADC() function. So need to divide with 1000.

// T = (0.0-A + sqrt((A*A)-4.0*B*(1.0-R)))/2.0*B;

// Break equation in small pieces

T = 0.0 - A;

T += sqrt((A * A)-4.0 * B * (1.0 - R));

T /= 2.0 * B;

temp = T; // Actual temperature value

}

If you have any question, ask feel free. I will totally devoted for your help.

Thursday, 6 April 2017

Normally open (NO) & Normally close (NC) contacts Introduction

NO (normally open) & NC (normally close) contacts Introduction

Often you have found NO, NC & COM in the electrical circuits. Most of the electrical circuitry processes depends on “Normally open” & “Normally close” contact.

NO – Normally open contact.

NC – Normally close contact.

COM – Common contact for NO, NC.

For example we take a SPDT relay, which have two coil connections, 1 Common, 1 NO & 1 NC connection. We gives +12v on COM and relay coil is off mode, NC contact will have +12v also because it is normally connected to COM contact and NO contact will not have +12v because it’s normally disconnected to COM contact.

If we energize to relay coil, NO will be closed with COM contact and NC will disconnect to COM. If we talk about any push type switch, push action will same as active relay coil.