Help with Temp/Press/Humidity

[clwill]

I am a relative noob with respect to electronic circuit design, though not completely incapable (soldering skills and so on). I have a fairly simple project and need some help/advice.

I have a data gathering system that accepts user-provisioned sensors. The system can provide either 5v or 12v to the sensor and requires the output to be 0-5v. It can calibrate the output in the software.

I need to capture temperature, barometric pressure, and humidity. I'd like to have some degree of accuracy, but in trolling through sensor catalogs most are fine (e.g. +/- 1C for temp).

But that's really the point. I'm overwhelmed. There are SO many sensors, I can't figure out what I need. There are all kinds of them, and the ones I find that are "simple" all are digital (output a stream via USB for example).

Can someone here help? I need some advice on sensors that you've used that would work for me. Or pointers to projects with designs for this sort of thing. Or ... any help at all, really.

Thanks in advance,
Chris

 

[KMoffett]

You need to define your range and environment for each type of sensor.

Ken

 

[clwill]

The sensors are for weather sensing, temp: 0-50C, baro: standard barometric pressures, humidity: ~0-100%RH. The sensors will be mounted in a very small package installed in a race vehicle. While a vibration intense environment, it's never operated in wet or freezing weather, and there is no need for anything more than minor water/weather proofing.

More info: the receiving device is a logger, it captures data at up to 1000/second, clearly many times faster than any sensor. I can sense as often as needed. While I'd like to maximize resolution (e.g. spread the results over the 0-5v as much as possible), I don't care about error rates, noise, etc. I will filter and calibrate all that in the resultant software. I just want the raw data from the sensors.

Is that enough info?

 

[KMoffett]

Just for our info...What make and model logger?
Do you have a maximum budget in mind?

Ken

 

[clwill]

It's a racepak system, but that's not relevant as I'm using their universal sensor system. Specs as noted.

Max budget is not a factor. Willing to invest what it takes to do it right.

 

[KeepItSimpleStupid]

Temp/RH are usually combined. I had to do environmental monitoring for an eventual paper a long time ago and I used a temp/RH sensor similar to these: **broken link removed**

This says 4-20 mA or 0-1V. 4-20 mA will be very common. It can be converted to 1-5 (I think) using nothing but a precision resistor )see DigiKey Corp. | Electronic Components Distributor | United States Home Page) at the logger end. This removes quantization errors at the low end. Current is very common because it's not affected by wire length. 24 VDC will also be common. The use of current output also tends to eliminate ground loops.

You may have to use a 5 to 24 DC-DC converter or 12 to 24 DC-DC converter to run standard sensors.

This might work for barometric pressure: **broken link removed**

But again, there are power supply issues.

Example converter: SKE15A-24: MEAN WELL: Power Supplies & Wall Adapters

You have to whittle out the specs that are appropriate. 5V power isn't popular for industrial control, 24 VDC is. Voltage output isn't popular either. Current output (4-20 mA) is a better choice and converting it to a voltage at the logger end. There may be differences between sourcing and sinking outputs. Sinking is more common.

Ploping a temperature sensor in the vehicle doesn't cut it either. Example: I mounted an outdoor thermister temperature sensor in the driveway for the HVAC system at home. You have to shieled it from direct sun and wind and you really cant attach it to anything if you want the air.

 

[clwill]

Thanks for this, some great places to start. Appreciate the pointers.

Ploping a temperature sensor in the vehicle doesn't cut it either. Example: I mounted an outdoor thermister temperature sensor in the driveway for the HVAC system at home. You have to shieled it from direct sun and wind and you really cant attach it to anything if you want the air.

Thanks, I'm all over this part of the problem. I have a plan, but I can't discuss it

 

[KeepItSimpleStupid]

Omega rebrands their stuff. There was only one time I wasn't happy with a product of theirs. It was an inexpensive TC scanner. It kept blowing up. Wheni got a hold of the service info,remember when you could, I found parts on the schematic that were not suffed in the product they sold. Just adding transient protection on the AC in, fixed them. This was nearly 30 years ago.

In another instance, I was able to add analog out to many meters by purchasing the parts and installing them.

 

[reidinstruments]

Hi CIWILL, this company makes the sensors that you are talking about and has great documentation. Try parallax and look in the sensor section. good luck