Arduino project housing help

Question

Hello everyone.

I'm new to the Arduino world and I need some help.

I've created my very first simple Arduino project [have a look]

It's really simple

It's using three sensors

1- MQ-5 for humidity sensing

2- LM35 for temperature sensing

3- BMP180 for pressure sensing

Let me explain the basic idea behind this project, every sensor has 2 leds, a green one and a red one, the greed led will be always on whenever the values of the sensors are in the right range

and the red led turns on when it over this range.

Now I want to cover this device to put it in the factory considering the following

1- It will be put in 100 degrees C

2- There will be dust

So here is what I need

1- A box to put the device in with lots of fans to keep the device cool in 100 degrees.

2- A cover for the wires to protect it from melting in 100 degrees.

3- A kind of texture to cover the LM35 and BMP180 sensors to prevent dust from going through them.

4- A kind of texture to cover the MQ-5 sensor to prevent dust but allow air to pass through.

Can you please suggest the best materials to get the job done perfectly?

Thanks!

gecoz · Answer

I'm not sure the sensors you are planning to use are suitable for your application. The LM35 will withstand 100C temperature, but definitely the BMP180 will not, as it is rated for the max temperature is 85C, and so the MQ-5 sensor, which is only rated at operating temperature of 50C. Trying to protect them, enclosing in any form of thermal protective cover, will likely result impairing the sensor sensitivity, giving you unreliable readings. You might get away with using the LM35 this way, but for the other two I'm afraid you will need industrial grade sensors, like for example this absolute pressure sensor. Unfortunately this will push up the costs for your project quite substantially. One question: MQ-5 is a Gas detector sensor, how are you going to use it as humidity sensor? Fabio. P.S: For the dust problem, as the-dubster correctly pointed out, you need to know the dust particle size to make any informed decision.

the-dubster · Answer

Good point, I hadn't even considered questioning the sensor selection. I was thinking about the Temperature Sensor - I thought about how easy would it be to encapsulate it within a metal sleeve for protection - like a simple temperature probe uses. I realised that the sleeve would affect the response time of the probe though - it has thermal mass unfortunately - it needs to be heated to transfer that heat to the probe (and of course it retains heat once the source is removed). I had a little play to see how badly it was affected. Sticking one in a cup of hot water took around 35 seconds to climb from ambient (23 deg C) to the water temp (around 85 deg C), not ideal. Worse still, when removed it took around 1:30 mins to return to ambient (it does slow when nearing the actual temperature measured in both directions, but you get a general gist of the effect). So, exactly as gecoz says, it will seriously impair the sensitivity. How quick you need it to respond - if it is slow enough - may negate this issue, or reduce its negative effect. Regards

the-dubster · Answer

One tiny question about thermal management, is there going to be cool air fed to the unit? If not then fans will merely circulate 100 deg C air through the unit as it will take external (hot) air to replace exhausted (hot)air, little or no cooling will take place (there needs to be a temperature difference for cooling to occur).

It is possible to find connecting cable that has a specification exceeding the maximum temperature you will face.

Could the box be located remotely and the sensors (wire length permitting) be placed in the environment you wish to monitor?

the-dubster · Answer

Re: Enclosure.

There are a quite a few options available, two common types are:

PC (Polycarbonate) temperature range around -20°C to 140°C - it also has excellent insulating properties.

ABS (Acrylonitrile Butadiene Styrene) again goes down to -20°C but not as hight as PC - also is not as tough or UV stable.

You could always use an Aluminium (Aluminum) case - something to be aware of, it would need physical thermal insulation from the Pipe to prevent heat conduction, also, even if not physically attached, heat would be transferred by convection. A plastic enclosure would insulate from this effect better than a metal one.

Re: Sensor mounting.

I suppose you could just hang the sensors into the airflow with suitably heat rated cable, alternatively you could mount the sensors at the end of PC tubes, this would insulate the cable and provide a secure mounting point for the 3 sensors in the tube.

Filtration is another area - one that will need a little more investigation. You would need to know the diameter of dust particles to best optimise the filtration material, you need to strike a fine line between blocking contaminants, maintaining uninterrupted airflow across the sensor, time between filter changes (it will clog) and thermal rating of the filtration material.

Hopefully this will give you something to work with, and, as it's taken me so long to draft ALL my reply, I'll find out if anyone else has provided a solution for you when I 'Add Reply'.

Regards

Arduino project housing help

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