MH Temperature Logger (1 Viewer)

[DBK]

August is supposed to be the silly season and so I have been doing silly things with my new Raspberry Pi.

What I have done is turned it into a temperature logging device which can be left in the MH and over a period it will measure the temeperaure in the MH and write it to a file. At the end I can take the file, load it into Excel and plot a graph showing how the temperature changed over, in this case, about 24 hours.

The graph above goes from about 3 o'clock on Saturday to about 3 o'clock on Sunday. The blip at the start of the graph is the device warming up as it was turned on. The vertical scale is of course degrees Celsius.

There is a serious side to this but it will have to wait for the winter. What I want to see is when the Webasto diesel heater is running how accurately does the thermostat hold the temperature? The reason is I suspect the temperature fluctuates quite a lot and this may be influenced by the position of the temperature sensor the heater uses as it is fixed to the wall near a small window in a corner. I have also noticed the temperature fluctuuations with the heater seem greatest i the first day or so of being switched on and after that, perhaps when the fabris of the MH has warmed up it seems to steady. The temperature logger I have made is software driven so I can set it to measure the temperature over several days if necessary.

I can add more temperature sensors to the Raspberry Pi and measure the temperature at floor level as well as say head hight.

However, it was interesting to see that the inside of the MH, parked outside with all the blinds drawn is going through at this time of year a daily temperature fluctuation of about twenty degrees.

 

[aldhp21]

Brilliant, been trying to find a reason to justify buying one of these.

Thanks
Alan

 

[DBK]

Brilliant, been trying to find a reason to justify buying one of these.

Thanks
Alan

I'll post a picture of it tomorrow and details of the bits needed, which were only a few pounds. It will be interesting to run it in the house too.

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[gozomike]

I have been doing silly things with my new Raspberry Pi.

Doesn't look that silly to me. I agree with your comment on the heating systems not holding the temp very steady so it would be interesting to see how much it moves.
Another interesting one, but perhaps difficult to get the cables in without causing damage, would be to monitor the temp in the van fridge along with the changes outside of it.

 

[laird of Dunstan]

Well done dbk ,I think that finding the optimum spot for the temperature sensor will be a frustrating task ,if you know any one with a thermal imaging camera ,that will help thermostats by their nature and build have what is referred to as a dead band , other wise they would be switching on and off constantly.

Your findings will be interesting

 

[DBK]

Doesn't look that silly to me. I agree with your comment on the heating systems not holding the temp very steady so it would be interesting to see how much it moves.
Another interesting one, but perhaps difficult to get the cables in without causing damage, would be to monitor the temp in the van fridge along with the changes outside of it.

That's a good idea. I have a fridge thermometer which has the sensor on a cable but it only shows the current temperature. But if I strip a few wires out of some Ethernet cable, which are thin then I could have a sensor in the fridge. That would be interesting to monitor especially in hot weather.

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[laird of Dunstan]

The type of sensor that you are describing is a thermistor it works on a measured resistance.
if we meet up at a meet ,I'll bring along a calibrated temperature probe and you can Check it's reading

 

[hilldweller]

August is supposed to be the silly season and so I have been doing silly things with my new Raspberry Pi..

DS1820s ? I scattered some round the house and could ring them up whilst away to check all was OK. Great fun.

I used a full blown PC but have a Pi and one day will convert it to Pi because it's so much neater. I have a Pi and a 7" LCD in a neat little box to play with in the van.

 

[DBK]

The type of sensor that you are describing is a thermistor it works on a measured resistance.
if we meet up at a meet ,I'll bring along a calibrated temperature probe and you can Check it's reading

I guess it must be a thermistor at its heart but the sensor, as Hilldweller identified, is a digital temperature sensor and gives a read out directly in centigrade, apparently plus or minus half a degree. But the absolute temperature is only half the the answer, I am more interested in the temperature fluctuation as we find in the mh it goes from comfortable to roasting without a happy medium.

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[DBK]

DS1820s ? I scattered some round the house and could ring them up whilst away to check all was OK. Great fun.

I used a full blown PC but have a Pi and one day will convert it to Pi because it's so much neater. I have a Pi and a 7" LCD in a neat little box to play with in the van.

A little screen would be useful for the van but a quick look suggests they are about a £100. I might look for a DVI to VGA adaptor so I can use the Avtex TV!

 

[hilldweller]

I am more interested in the temperature fluctuation as we find in the mh it goes from comfortable to roasting without a happy medium.

The answer is PID but even that will not cope if you keep opening the door.

 

[hilldweller]

A little screen would be useful for the van but a quick look suggests they are about a £100. I might look for a DVI to VGA adaptor so I can use the Avtex TV!

I under half that off ebay direct from China.

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[DBK]

The answer is PID but even that will not cope if you keep opening the door.

I guess the problem is also that keeping a stable temperature in a house, surrounded by thick walls is a lot easier than a MH with very little actual mass.

 

[TheBig1]

was looking at some raspberry pi kit just the other day. touchscreens with combined cases are only about £30 on ebay. was costing out building a combined NAS server and media player to use at home or pop into the van when going touring

 

[hilldweller]

I guess the problem is also that keeping a stable temperature in a house, surrounded by thick walls is a lot easier than a MH with very little actual mass.

Definitely. But a_cunning_plan with a Pi has a chance. You could wire in the hab door and be prepared for a drop. How you would control a Truma is another matter. Our Truma has a thermistor above the hab door, cleaver that, it spots the cold air. You could wire the thermistor through a relay controlled by Pi, set the Truma temp very high the fool it into thinking it was very high. But if the Truma is also running a PID anything could happen.

You will have noticed Techo's Italian Truma controller, this guy seems to have got inside it.

For inspiration..........I have a little computer wired to doors and a PIR, so an alarm, two relays control inside and outside lights, they come on when the alarm is triggered so we find out way in in the dark. It has a clock, alarm clock, egg timer and finally a door bell. So get programming.

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[tonyidle]

A little screen would be useful for the van but a quick look suggests they are about a £100. I might look for a DVI to VGA adaptor so I can use the Avtex TV!

Sensors are normally a thermocouple for measurement purposes. Sensors for heating systems tend to be thermistors.

 

[DBK]

Sensors are normally a thermocouple for measurement purposes. Sensors for heating systems tend to be thermistors.

I'm using a thing called a DS18B20 digital temperature sensor, it has as its name suggests a digital output but I am not totally sure how it measures temperature although I guess it is a thermistor.

 

[laird of Dunstan]

For some thing like a trauma you would have to build in a run on timer to the fans ,if you just kill it using a relay ,the latent heat will reduce the life of the unit.

"Laughing " I'm sitting at a pc checking ,chillers,boilers ,fan coils and AHU,s they are all controlled by software .

When I get my new Mh ,I'll have to have a fiddle

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[laird of Dunstan]

I'm using a thing called a DS18B20 digital temperature sensor, it has as its name suggests a digital output but I am not totally sure how it measures temperature although I guess it is a thermistor.

If it's cheap it will be a thermistor ,the expensive ones work on a 4 to 20 milli amps signal and are very a curate ,it will have an internal scaling , in other words , say when it is sensing one resistance it would read 21 Dec for example ,when due to temperature change ,the resistance changes and it reads accordingly

Sorry if you know this stuff already

 

[Taran_Las]

DS18B20 Datasheet indicates accuracy to 0.5 degree.

 

[hilldweller]

I guess it is a thermistor.

Just for the sake of accuracy, nothing that archaic. It is a very complex chip that will use a silicon junction on chip to sense temperature. Every one is individually numbered by laser but I'm not sure if they also calibrate the temperature at the same time.

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[tonyidle]

For some thing like a trauma you would have to build in a run on timer to the fans ,if you just kill it using a relay ,the latent heat will reduce the life of the unit.

"Laughing " I'm sitting at a pc checking ,chillers,boilers ,fan coils and AHU,s they are all controlled by software .

When I get my new Mh ,I'll have to have a fiddle

The Truma is interesting. It's sensor is a thermistor (which just happens to be the same one used in mobile phone batteries - don't ask me how I know that). The heater senses the variation in its resistance due to temperature change as you would expect. Under normal conditions as the set point is reached the heater turns down to a lower setting. If the air temperature does not fall the heater switches off completely after a few minutes. The effect of this is that under normal conditions the heater doesn't often turn off completely - it modulates its output so that the vehicle occupants aren't subjected to large temperature changes. As an aside if the sensor fails in such a way that the heating stays off (which is what happened to mine) disconnecting it will cause the heating to turn on. At least knowing this means you can keep warm whilst sourcing a replacement for it.

 

[DBK]

Just for the sake of accuracy, nothing that archaic. It is a very complex chip that will use a silicon junction on chip to sense temperature. Every one is individually numbered by laser but I'm not sure if they also calibrate the temperature at the same time.

There is a lot of information on it here: http://cdn.sparkfun.com/datasheets/Sensors/Temp/DS18B20.pdf
But it doesn't really say how it works other than saying it has a "direct-to-digital temperature sensor". The very last page shows a graph which suggests the mean error is fairly small - or at least good enough for my purposes.

 

[hilldweller]

For some thing like a trauma you would have to build in a run on timer to the fans ,if you just kill it using a relay ,the latent heat will reduce the life of the unit.

I didn't mean that. If you fiddle the resistance of the thermistor with a relay and maybe a resistor then all you are doing is altering the temperature the Truma thinks it is.

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[DBK]

I said I would post a picture of the device. The actual temperature sensing thing is the little component looking like a transistor on the left of the resistor. Obviously, this is not exactly a productionised version!