Heat Resistor (NTC) and Cold (PTC)

A. Heat Resistor (NTC)
NTC (Negative Temperature coefisien) is a resistor with a negative temperature coefficient is very high. Thermistors of this type is made of oxides of transition metal group element (eg Fe2O3, NiO CoO and others – others). Oxide – oxide has a very high resistivity in pure substances, but can be transformed into a semi-conductor by adding a bit of ions – other ions of different valence.

The nominal price is usually set at a temperature of 25 ^° C. Change in resistance caused by non linieritasnya shown in diagram form of resistance with temperature, as shown in Figure 3.10 below.

Whenever possible to find a NTC thermistor to meet all the required NTC prices, sometimes – sometimes much more economical when combined or adapted some NTC prices of existing resistance in series with one or more NTC thermistors that we have. Sometimes, by adding a series resistor and parallel to the NTC, and we can get the price of NTC thermistors standard that we need.

Had can not then we need to find a special type NTC thermistors that we need. So if all combinations of resistors that we have done we did not get the price of NTC standard that we need, so in this case we need to look for the NTC in accordance with the specifications we need. In a series where there is a NTC, then additional series resistor is often a lot of benefits.

The following example will show and explain a result of a combination between the NTC resistor .Anggap ordinary course now we are in need of NTC thermistors with prices ranging from 50 Ωpada 30 ^o C and 10 Ω at 100 ^° C. Of course, standard type that have such characteristics are not included in our program. Yet, we do not need to worry because this problem can be overcome by a single NTC resistance standards and the usual two.

Suppose now that there is an NTC with cold detainee is 130 Ω, and let us plug with a combination of series and parallel with an ordinary resistor at 6 Ω and the other at 95 Ω resistor, as shown in Figure 3.11. From this combination, we will need the resistance at a temperature of 30 ^° C and at a temperature of 100 ^° C will be fulfilled.

Figure 3.11. Circuit characteristics Deviation

B. Cold Resistor (PTC)
P (ositive) T (emperatur) C (oefficient) or PTC thermistor is a resistor having a positive temperature coefficient is very high. In some ways this is different from the NTC PTC as outlined below:

• The temperature coefficient of the PTC thermistor will be positive only between certain temperature range. Beyond this temperature range, the temperature coefficient can be zero or negative.
• The price of the absolute temperature coefficient thermistor PTC, almost the whole event much greater than that of NTC thermistors.

Figure 3.12. Physical form and the symbol PTC

Figure 3.12. Physical form and the symbol PTC

It should be noted that the resistance is in a logarithmic scale and resistance change ranging from a few hundred ohms at a temperature of 75 ^° C and several hundred kilo ohms at a temperature of 150 ^o C.