Resistor

Every circuit have a property of resistance at which they do operate. In a circuit if we have engineered resistance and it does its function properly then this resistance is called a load resistance or loading device. Resistance is used to limit the current and also to produce a voltage drop in electrical circuits. Also resistance is used to measure some quantities like pressure, temperature and current flow in computer systems of automotive. There are three types of resistors. Fixed resistance, variable resistance and stepper resistance. 

Fixed resistors:

Fixed resistors have fix value. They are coming in different ohmic values and power rating (wattage). They are made of carbon or metal oxide. They have fix value and they are used to create a voltage drop depends upon current flow and also they are limiting current through the circuit they are connected in. Fix resistors has value written on them if they are of big wattage rating. Otherwise they have a color code on them if they are of small wattage rating. They use four or five color bands to show their resistance value. If there are four bands on a resistor, the first two bands shows digits and the third band is multiplier band. Whereas the fourth band shows the tolerance of resistance value in that specific resistor. This tolerance is normally 5% to 10% in most resistors. Some very good quality resistors have tolerance as low as 1%.

Resistance color code table

Variable resistor:

As the name employee the variable resistors are not fixed resistance. The value of those resistances can be changed through a knob or a shaft provided on them. There are infinite values can be selected on the given range of a variable resistor. They are both rotating type and sliding type. Both have different used in electrical and electronic circuits. They are same like radio or stereo volume control. They have usually three pins or three terminals. The two terminals have fixed resistance in between them and the third terminal is wiper or the variable terminal of potentiometer and it provides the variable resistance value. They are also available in different values and power rating sizes. The very common purpose of the variable resistance is to make the voltage divider network. In such a case one end of the resistance is connected to the positive voltage supply and the far end is connected to the ground or return or negative of the supply. The third terminal is providing the divided voltage or the variable voltage in such a case. Such voltage dividers have many uses. They are used as throttle position sensor, tank fuel level sensors, cng tank level sensor and accelerator position sensor.

Variable resistance or potentiometer

Stepper Resistor:

Stepper resistor is a combination of fixed resistors arranges in steps. For stepping a switch is used to change the resistance value. This type of resistance have also three terminals same like variable resistor. But stepper resistor has limited and known number of resistance steps. This type of resistance is used in automotive fan speed control. As in most vehicles there are a few steps of speed control is provided on the dashboard as climate control. By changing the steps of switch we can vary speed of the fan motor hence air is controlled through the fan motor speed. The way is controls is we add resistance in the fan circuit due to which a voltage drop is produced on that resistance and fan motor is taking limited current and it spins at lower speed.

Stepper resistance. Car fan motor control system schematic