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Test/Measurement Electronics Help?

The specs says it uses an I2C output for the data. The solution that comes to mind to me would be to use an I2C to RS232 converter to send that data to a PC. Google brought up several options. Other options would be using a small microcontroller like the TI MSP430 (only one I am really familiar with) to read in the I2C data, format it, and then send it to an LCD display, many of which also use I2C. Or, simpler may be using an experimenter's board like an arduino which are pre-wired for I2C inputs and outputs. The last two options at least would require some electronic assembly and programming.

I can try to provide some more details if you like, but I left engineering to be a fireman, so I'm sure there's somebody more knowledgable than me :D A little research on I2C may be a good start.

Chris
 
I like the Arduino controller. Easy to do and plenty of "how-to" info on the web for non-engineer types.

http://arduino-info.wikispaces.com/PROJECT-Temp-Humidity-Display

Once you're done prototyping, the whole thing can be neatly packaged in a small housing that could be mounted to your instrument panel.

You will have to make a powersupply for it if you're gonna wire it to ship's power.
 
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Dan,

It depends on how you want to use the information form the sensor. If you want to be able to display it in real time in the cockpit you will probably need a microcontroller of some sort, a display, power supply, and some software written and programmed into the microcontroller. The Arduino controller is pretty easy to configure for an application like this.

Sparkfun has several humidity sensors and there is a good support community there that may be of use to you.

Here is a link to one humidity sensor and some Arduino application information for a humidity sensor application.

https://www.sparkfun.com/products/10239


If you want to record the information for later analysis and review you will probably want a superset of the above.

If you want to just display the data on a laptop there are several solutions as described on the earlier post.

If you can be a bit more specific in what you want to do the community can probably get you closer to a viable solution.

Phil
 
humidity sensor

Hi Dan,
It would need some code somewhere, either with a I2c to RS232 adapter or directly to a LCD display. I did a similar project using a couple of pressure sensors for cowl pressures using a Microchip product.

Let me know what the end game is for this unit, but bottom line is some coding will likely be necessary.
 
Dan, I saw your temp/humidity posting and thought that I'd share how I'm starting a simple Arduino project. Like you, I'm not an electronics expert. I'm an old retired stress engineer. This is new to me.

I ordered a Sparkfun Inventor's Kit for Arduino - V3.1 from Amazon for $100. They were out of them at Sparkfun locally (Sparkfun is a local company). Several other companies make starter kits. Mine should arrive Wednesday.

I downloaded the "IDE," or Interegrated Development Environment, the editor in which we will write our programs and upload them to the Arduino. I got that from http://www.arduino.cc/en/Main/Software.

There are numerous books and PDFs that you can get. The www.arduino.cc site has a language reference and the IDE and a starter's kit have examples.

When I get my gadget working I'll buy the Sparkfun Pro Mini, a tiny Arduino. https://www.sparkfun.com/products/11113. This will be the unit that I'll hardwire. This suggestion and the next item were recommended by the people at Sparkfun.

It needs a gadget to connect your computer to it, though, to upload the program. That's https://www.sparkfun.com/products/9716. It won't become a part of the flight system.

Other devices like sensors, resistors, switches, displays and so on, are usually also needed and are up to you.

Good luck!
Dave
 
If you can be a bit more specific in what you want to do the community can probably get you closer to a viable solution.
Click to expand...

Thanks gentlemen. Don't mind a learning curve, but this time I'm looking for a quick approach.

App is determining the dew point of typical engine breather output, which can be derived from temperature and RH. That little sensor would slip right inside the hose and measure both at the same point.

Already have two temperature sensors in the lines. As expected, breather gas leaves the accessory case a bit warmer than oil temperature, and cools some as it passes through the separator. If separator outflow temperature is higher than dew point, water return to the engine case is not possible. One measurement is worth 1000 opinions, yes?
 
Dan,

Take a look at this. You should be able to hook it up to a 4-5.8VDC power source and connect the output to your handheld voltmeter. Use a simple printed table to determine RH. The Sparkfun breakout board makes attaching the wires easier.

https://www.sparkfun.com/products/9569



The datasheet below has the conversion chart.

https://www.sparkfun.com/datasheets/Sensors/Weather/SEN-09569-HIH-4030-datasheet.pdf


Here is a way to get the 5V from your aircraft power buss.

https://www.sparkfun.com/products/114


Phil
 
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Good stuff all, thanks, keep it coming.

The analog sensor approach is interesting. I have some 5V supply chips. It assumes 25C so a correction for actual temperature will be needed.

That particular sensor is available in open and shielded models. I'm sure oil, lead, etc would screw up even the shielded version eventually, but I just need short term measurement.

Any thoughts on physical, non-electronic measurement? Really, really simple example; I bagged a sample of breather outflow gas in a ziploc. It condensed fine water droplets on the inside of the bag when it cooled to ambient, a bit over 90F yesterday.

rj1bv7.jpg


That would lead me to think the dew point of the sample was above 90F, but oddly enough, almost all of the condensate re-evaporated into the bagged air after some time had passed. Hmm..time to review the physics....
 
I am a bit of a Psychometric geek, you can keep the harmonics Dan.
I use a Onset Hobo recorder for temp and humidity. Don't know how to get one to work in your testing though.
You are really measuring dry bulb and wet bulb to get RH or DP.
The best way to get WB physical, non-electronic measurement is dry bulb and then a dry bulb sensor with a wet wick. (scrap of wet shoe string safety wired to the end of the bulb. I just don't how you could keep it wet and have a good airflow over it in your case.
 
Dan,

Here a a couple of links to another alternative that you may want to look at. I am sure that you can find these types of instruments on ebay as well.


Ambient Weather WS-HT350 Fast Response Air Thermo-Hygrometer with Wet Bulb Psychrometer, Dew Point Meter - $49.99


Psychrometers
http://www.ambientweather.com/psychrometers1.html



The below is an example of an Onset Hobo datalogger as mentioned above that may work:

HOBO U23 Pro v2 External Temperature/Relative Humidity Data Logger - U23-002 - $199
http://www.onsetcomp.com/products/data-loggers/u23-002

I do not have any affiliation with these companies or products.

Phil
 
Dan

Depends on how fancy you want to get. An Arduino speaks I2C natively and you can simply write a couple lines of code to output the data, plug a USB into a laptop, and turn on serial monitor. You can get a 3.3v or 5v Arduino Pro Mini or clone for $10 and the programmer interface for about the same, whip something up on a bread board in no time at all.

If you want to get fancy, you could consider a Raspberry Pi or Beagle Board both of which I think also support I2C natively, and are fully function Linux systems, even with Ethernet and a fully function GUI for under $50! You could output the data over WiFi with a dongle or have it on a web page and use Cacti or MRTG to to graphing over time etc etc.

Essentially with Arduino and Pi, discrete electronics are almost a thing of the past and fully programmable microcontroller systems are as simple as Lego.
 
Why not just get an analog output sensor and use a multimeter/scope/analog input on your EFIS or EMS?
 
Dan,

You didn't say if it was for your plane or a test platform. I know you do lots of bench testing.

The Arduino boards have many "shields" or daughter card that can be found for a wide variety of applications. If you look around you might be able to find one that has exactly what you want and often they come with the code to run them. These boards are primarily used by hobbyist but they can be a simple way of building a widget.

Your problem can be broken down into two problems. The first is reading the data from the sensor. The second is providing the data to the user. You didn't mention if you wanted to display it on a small LCD or similar display or if you want to be able to log it to your PC or both. If you want everything I suspect you wont be able to find exactly what you want. I recently bought an Arduino board with a shield that is meant to control a reflow oven. This unit has a display, a thermocouple interface and a USB output for logging the data. It's pretty close to the hardware that you need, but the program is meant for controlling a reflow oven. You would have to write your own application.

PS I got a laugh out of the zip lock with the thermometer.
 
Dan I don't think your answers are on the psychometric chart. That is for human temps and I believe you will find that the dew point is somewhere between 140F and 180F. If I am reading this chart right it is off the range of the chart. It might be more appropriate to look at the steam tables.

I know you want to measure, but have you considered an isooctane and air equation and just calculate the % water. Then from molar ratios and partial pressures determine the dew point? The range could be calculated from various intake air humidities, and air/fuel ratios to get it more precise.

In our test lab we used an expensive condensing mirror to measure such things, not practical here.:(
 
BillL said:
Dan I don't think your answers are on the psychometric chart. That is for human temps and I believe you will find that the dew point is somewhere between 140F and 180F. If I am reading this chart right it is off the range of the chart. It might be more appropriate to look at the steam tables.

I know you want to measure, but have you considered an isooctane and air equation and just calculate the % water. Then from molar ratios and partial pressures determine the dew point? The range could be calculated from various intake air humidities, and air/fuel ratios to get it more precise.
Click to expand...

Funny you should mention that. A simplified chemistry-and-thermo approach says somewhere around 130~135F, depending on actual water percentage in the breather gas. For now I'm assuming breather gas is much like exhaust gas, about 13% H2O. We can't know the exact number of hydrogens (although isooctane probably isn't far off), because gasoline is a blend. The assumption will do for now. I'll measure later, as all my helpful friends have gotten me interested in playing with little bitty computers ;)
 
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Dan also look at the mbed platform microcontrollers. I have been using an mbed LPC1768 and have loved it.
 
DanH said:
Funny you should mention that. A simplified chemistry-and-thermo approach says somewhere around 130~135F, depending on actual water percentage in the breather gas. For now I'm assuming breather gas is much like exhaust gas, about 13% H2O. We can't know the exact number of hydrogens (although isooctane probably isn't far off), because gasoline is a blend. The assumption will do for now. I'll measure later, as all my helpful friends have gotten me interested in playing with little bitty computers ;)
Click to expand...

OK, I got about 10% H2O by a molar ratio. Good, you have a ball park to start. Have you considered taking the sample and then heating it back to measured temp and getting a lab to measure the content? The sample bags are a little different than a zip lock to keep HC elements from adsorbing to the surface, but for water, a zip lock would be fine. You can attach a stainless boss to the bag (like a suction tap for bagging composites) then use teflon line for the sample line. It would be reheated prior to testing. You would not care about the adsorbed exhaust components so it should be fine for water along as the temp stayed high, you could insulate it. You could get an adsorbent in the bag for water and weigh it, but then you would have to measure the volume pretty precisely. Maybe bubble it in an upside down graduated cylinder? Seems like to many small variables for accuracy.

A bagged sample would allow some better lab work or test it on the bench at home with easier access to power supplies and breadboarded components. Just stick it in an easy bake oven, stabilize back to temperature, and pull the sample through the test device.

I had some Russian engineer use an evacuated wine bottle for a sample once. It worked pretty well. We walked in the mine (in Siberia), held the evacuated bottle over is head with a cork and pulled it out. I sucked in the sample and he reinstalled the cork. Took it back to the lab and pulled out the sample for lab analysis. Crude, but elegant solution. Maybe OK for this use if used carefully.
 
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BillL said:
OK, I got about 10% H2O by a molar ratio. Good, you have a ball park to start.
Click to expand...

Yep, and I appreciate the check.

The other ballpark is temperature. Most of the common humidity/temp sensors don't have enough temperature range. I have a pair of LM135's installed inside the 3/4" breather lines, one at the accessory case exit and one at the separator exit to the exhaust tap. Initial readings were 197F at the engine and 155F at the separator exit, at cruise power, oil temp at 185F, and about -3.5 Hg suction. In-flight RH measurement will require a sensor capable of 100C, minimum, as I want it in the hot hose, prior to any possibility of condensation. The CC2D355 referenced in the first post claims 125C.

I had some Russian engineer use an evacuated wine bottle for a sample once. It worked pretty well. We walked in the mine (in Siberia), held the evacuated bottle over is head with a cork and pulled it out. I sucked in the sample and he reinstalled the cork. Took it back to the lab and pulled out the sample for lab analysis. Crude, but elegant solution. Maybe OK for this use if used carefully.
Click to expand...

Ran across a paper while looking for literature, subject being air quality in Russian mines running diesel engines. I know Cat is world-wide, but Russian mines in Siberia?

I should have been an engineer. I don't get to go anywhere ;)
 
Dan,
Some equipment I use for drying polymers has high temp rel hum sensors. I'll try to find sensor info. Doubt it will solve the oil contamination prob posted early in the thread.
 
I've been doing some thinking. In the context of breathers and dew points, I may have a very practical approach. Hang tight.
 
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