| ADVANCED LESSON 26 | |
| LEARNING OBJECTIVES and NOTES | |
| Temperature effects | |
| 3m.1
Recall that temperature has an effect on the value of components. Those
with negative coefficients will reduce in value as temperature rises
whereas those with positive coefficients will increase in value.
Understand the effect this will have on tuned circuits and remedial
measures. If the coil and capacitor in the tuned circuit of an oscillator are warmed up the metals in these components will expand, the value of the components will change and the frequency will change. Components with a negative coefficient will reduce in value. Components with a positive coefficient will increase in value. The problem can be overcome using the following methods: Use a combination of positive and negative coefficient capacitors so as one expands the other contracts. Reduce the temperature inside a piece of equipment by using adequate ventilation and possibly fans to take away warm air. Although we have said that crystals are very stable, they are not immune to the effects of temperature change. In some equipment, the crystal is placed inside a mini oven. This maintains a constant temperature and keeps the crystal on frequency. Choose capacitors that maintain their capacitance over a wide range of temperatures. For example ceramic NPO capacitors are used in oscillators and tuned circuits because they are less affected by temperature. |
Crystal oven with top removed
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