NTC sensor

[pma]

Firstly, can anyone tell what this is and what it's function is?

Secondly, What are symptoms of it's failure?

Thirdly and lastly, how easy are they to change (on an Ideal Classic NF60 Boiler)?

Thanks

 

[baxpoti]

NTC THERMISTORS
are composed of metal oxides. The most commonly
used oxides are those of manganese, nickel, cobalt,
iron, copper and titanium. The fabrication of
commercial NTC thermistors uses basic ceramics
technology and continues today much as it has for
decades. In the basic process, a mixture of two or
more metal oxide powders are combined with
suitable binders, are formed to a desired geometry,
dried, and sintered at an elevated temperature. By
varying the types of oxides used, their relative
proportions, the sintering atmosphere, and the
sintering temperature, a wide range of resistivities
and temperature coefficient characteristics can
be obtained.

 

[corgiman]

NTC THERMISTORS
are composed of metal oxides. The most commonly
used oxides are those of manganese, nickel, cobalt,
iron, copper and titanium. The fabrication of
commercial NTC thermistors uses basic ceramics
technology and continues today much as it has for
decades. In the basic process, a mixture of two or
more metal oxide powders are combined with
suitable binders, are formed to a desired geometry,
dried, and sintered at an elevated temperature. By
varying the types of oxides used, their relative
proportions, the sintering atmosphere, and the
sintering temperature, a wide range of resistivities
and temperature coefficient characteristics can
be obtained.

thats all well and good but do they make the tea?

 

[stevesey]

N.egative T.emperature C.oefficient resistors basically. That is as the temperature goes up the resistance decreases. Uses - well combined with a transistor they make a simple fan controller so that as the temp rises the fan goes quicker (e.g auto fan speed controller for a PC).

Do you know where they are? I guess are used as the the flow and return temp sensors, it would be easy enough to knock up a circuit that used the difference between two of them drive an output to the gas valve and regulate the gas supply appropriately (of course the latest boilers are microprocessor controlled - but probably use NTCs as the sensors).

 

[Agile]

I guess are used as the the flow and return temp sensors, it would be easy enough to knock up a circuit that used the difference between two of them drive an output to the gas valve and regulate the gas supply appropriately (of course the latest boilers are microprocessor controlled - but probably use NTCs as the sensors).

Wow, clever design technology there!

But would it not be simpler to use a PTC sensor and just put it in series with the gas valve modulating coil so you dont need anything else?

Trouble is that if you use a micro controlled boiler then you have to have ADC inputs with the NTC sensors. Whilst you are about it you could have some simple look up tables to see whats on the table for breakfast!

 

[pma]

Thanks all for the info!!

I had a theory that my boiler cutting out when there was demand for HW/CH (but HW in particular) was due to overheating and not firing up agin unless the boiler is switched off for a period of time could have been this sensor.
Not so sure now as the cutting out could be the sensor working ok?!
Perhaps the PCB is the item stopping it from firing up again?

 

[ChrisR]

This is typical - many boilers ntc's have similar resistance curve.

NB this is from a COMBI boiler, yours isn't.

And yours hasn't got an NTC, it's got a thermostat!

Check circulation.

 

[stevesey]

I guess are used as the the flow and return temp sensors, it would be easy enough to knock up a circuit that used the difference between two of them drive an output to the gas valve and regulate the gas supply appropriately (of course the latest boilers are microprocessor controlled - but probably use NTCs as the sensors).

Wow, clever design technology there!

But would it not be simpler to use a PTC sensor and just put it in series with the gas valve modulating coil so you dont need anything else?

Trouble is that if you use a micro controlled boiler then you have to have ADC inputs with the NTC sensors. Whilst you are about it you could have some simple look up tables to see whats on the table for breakfast!

How with one sensor (+ve or -ve) could you measure the flow/return difference? That would be clever After posting I was researching for a boiler replacement and noticed that several service diagrams referenced NTCs on flow and return.

I suspect the most of the micro controllers used in boilers have ADCs built in. Of course with micro controllers NTC or PTC is irrelevent as the software can be designed to cope with either.