# NTC PTC thermistor symbol

What is the reasoning behind the arrows on the circuit symbols of NTC (up and down arrow) and PTC (two up arrows)?

• Can you add a picture?
– MCG
Feb 21, 2019 at 10:18
• I added the picture from the answer below. Feb 21, 2019 at 22:20

I've never thought about it, but I think that the arrows describes how the thermistor behaves.

NTC: internal resistance decreases with a rise in temperature.

PTC: internal resistance increases when the temperature rises.

So, the first arrow represents the temperature and the second one the internal resistance.

• Well, technically, either arrow can represent either thing, as long as one is temperature and the other is resistance ;) Feb 21, 2019 at 22:21
• @Toor not true for the NTC picture. The left arrow on that must be temperature and the right hand arrow must be how the resistance reacts to temperature change. Otherwise the diagram is incorrect.
– MCG
Feb 22, 2019 at 11:15
• Logically untrue. If resistance falls as temperature rises, then that also means that resistance MUST rise as temperature falls.What's important is they move on opposite directions relative to each other, not the particular direction any one variable is being moved so it doesn't matter which arrow is which. The implication in your statement just now was the NTCs can only ever decrease in resistance which we both know is false. Feb 22, 2019 at 14:58