Hello all,
I am going to use some heat trace cable to increase the temperature of wood studs in embedded beams a home for a project. The wood is expected to increase in relative humidity to very high level. It is known that heat can be applied to the wood studs using heat trace cable to dry them out. There are going to be 3 seperate cables in this experiment in three different areas of the house.
I was thinking about using an ardunio and hooking up a humidity sensor probe. the thinner the diameter, the more ideal. If the humidity reaches 70%, then the system should be switched on. I haven't decided the stop humidity % yet.
If the project is too complicated, I would consider switching on the heating myself in a simple non-controlled circuit, and having the ardunio just monitor the humidity and do nothing else.
My goal is that I would just need the arduino to tell me what the current humidity reading is on a digital 7 segment display. The sensitivity of the sensor itself is not important, but the diameter of the probe is. pencil thickness or smaller. I would consider logging and control at a later date when i have time. what other components do i need? If there is kit out there already that will do this job that is not too costly rather than using an arduinno, I would prefer to use that. What ever is simplest.
highest priority: What humidity sensor can i use? and generally where could i buy one? lower priority: (can be done later) How would I hook this up to the arduino?
At the moment, the priority is installing the proper humidity sensor as the drywall is going to be installed soon, the controls can be done later.
sittingonit:
but what if there are three different humidity sensors? arduino the best choice?
DHT11 sensors measure temp and humidity and are much cheaper than those Honeywell ones ki4amd linked to. Less accurate but probably good enough. Unfortunately they are about 0.5in x 0.6in x 0.2 in. Is that too large?
Multiple sensors could be attached to an Arduino, along with perhaps a 16x2 character lcd display (giving much more room and flexibility than 7-segment displays).
Your link to the "heat trace cable" did not work for me, so can't advise on how to control them, but something will be possible I'm sure. Maybe a relay board.
Is Arduino the "best" choice? Well, its a choice, but you will need to put some effort in constructing and programming. Lots of help here for those that are keen to learn. A lot less than $500 too!
Hi, it would be advisable to make the access to the sensor as easy as possible, because they will not last forever and you will be finding that they will have to be replaced.
When you are measuring humidity in the wall, you are measuring the air humidity not the wood, it would be worth having a small fan to circulate the air before each measurement, so that not just a local reading is made.
You would only need to read every day or so, and only need a couple of minutes for stable readings each time.
If you are aiming at drying the wood, then you will need to get rid of the humid air, so a circulation system will also need to be added. Just heating the wood will only push the moisture into the air, and it will only go back in when it cools. ie Waste of energy.
the best method is using a probe that are pins, and measuring the resistance of the wood is what is needed and not the air, which would give an incorrect reading.
I made a mistake it should read "moisture content pin sensor" and not "humidity meter"
I am not going to explain the science of why this works as it takes too long, but past research shows that drying occurs over the course of many weeks to several months using this method in both the lab and on site. It is not an instantaneous solution like using a hair dryer on your hair, that is not the goal.
this would be great if i knew what type of pins can be used with this.
it would be advisable to make the access to the sensor as easy as possible, because they will not last forever and you will be finding that they will have to be replaced
great idea!
DHT11 sensors measure temp and humidity and are much cheaper than those Honeywell ones ki4amd linked to. Less accurate but probably good enough. Unfortunately they are about 0.5in x 0.6in x 0.2 in. Is that too large?
it may be pushing it every so slightly. If it was possible to have a longer sharp probe that can be shoved in one or two holes.
I have one of these moisture meters. As you can see the probe is a small pin. the pins are shoved into the wood. The pins can also be removed on this unit very easily, and new probes can be screwed on. If this probe had screws that were 3 inches long, I would say that my problem is almost solved, but it can only be used at the point of use which is no good. I can't cable it to the control panel...I think.
Ok, so you want to measure moisture content in the wood by measuring its resistance. Completely different question, all the suggestions we have given so far are sensors for air humidity and not whst you need.
In theory you just need to knock a pair of 3 inch nails into
each place you want to measure. The Arduino could then measure the resistance of the wood between each pair of nails. Each pair would have to be separately calibrated, as the exact separation and angle of the nails would change the reading. The big problem would be what to calibrate against? Your meter's short pins only measure on the surface, but the moisture content could be different 3 inches in.
Ok, so you want to measure moisture content in the wood by measuring its resistance. Completely different question, all the suggestions we have given so far are sensors for air humidity and not whst you need.
This is true, we are getting on the right track.
In theory you just need to knock a pair of 3 inch nails into
each place you want to measure. The Arduino could then measure the resistance of the wood between each pair of nails. Each pair would have to be separately calibrated, as the exact separation and angle of the nails would change the reading. The big problem would be what to calibrate against? Your meter's short pins only measure on the surface, but the moisture content could be different 3 inches in.
This sounds like a good idea for a project, but I am not sure if it is the most effective way. There has to be a piece of kit out in the ether that is either a) standalone b) or can be hooked up to the arduino
Stainless steel nails driven in a specific distance and a specific distance apart would seem to be appropriate for sensing.
Calibration is of course, the difficult-to-impossible matter, best to say you build the hardware and then perform tests on known pieces of raw and adequately cured wood to determined the corresponding values and just use those.
Note that resistance sensing using the Arduino analog pins is dead easy, but in all cases using resistive moisture sensing, in order to prevent electrolysis (and local drying of the material where the electrodes are) you need to use a system that only applies the voltage very intermittently (say, hourly or less), only for as long as required to make the measurements (a millisecond or so) and then reduces to zero (or short-circuits) the voltage across the electrodes.
This can be done by using a digital pin to feed a resistor (about 1 megohm) which connects to the analog pin which also connects to the electrode (the other electrode being grounded). To measure, the digital pin is set high (Vcc) and after a millisecod or so, an analogRead performed, then both digital and analog pins are set to their resting state as outputs low (since the analog pins that you use are also digital pins).