LM34 “Short Distance” Temp. Device using CB2xx PLCs.

[max]

Title: LM34 “Short Distance” Temp. Device using CB2xx PLCs.




by
User Batman!




Thank you!


Download Here:
http://cubloc.com/users/cubloc_CB2xx_LM34F_R1.zip

[Chip-Circuit]

The wiring shows a simple connection. if one adds a cap in the line, preferably close to the sensor, it will improve reading.

I have tried both, on the PCB and at the sensor, but have not tried to use these over about 20 feet from the board.

Dave

[batman]

The LM34 is really a Temperature to Voltage sensor and a very long line (capacitance) will cause problems. (per spec. sheet) I am very surprised you got it working at 20 feet. That's why I called it the "short distance temp device. The AD590 is "current driven" and it can used at much greater distances. (The long distance temp device)

[Chip-Circuit]

I have an array of 24 sensors. each is run on 18ga, twisted shielded, with the longest line being 24 feet.

This is for a 24 point data logger.

We used the LM34 after much discussion. We calibrate them by putting them inside of a box and letting them all stabilize, then add any correction factors.

then heat the box with a lightbulb and let is stabilize again.

Seems to work well enough.

We do use 12 bit ADC's as the BS2 is the microcontroller used.

Dave

[PatM]

I use the LM34 remotely as well, it just needs a bit of attention to deal with line capacitance problems.

Put a 1K resistor on the power supply leg (+VS), and 3K on the signal output. Either solder resistors right to the legs or make a little PCB - then cover everything with shrink tubing. No need for shielding unless you're running extremely long cables or are in a hellishly noisy RF environment.

I use two LM34s on a temperature datalogger with 20 feet of 4 conductor telephone wire on each sensor - no problems at all. I did take one 60 feet (added two extensions) and didn't notice any problem with that either.

[Chip-Circuit]

I would like to make a temperature data logger with a couple sensors, and then read that into a SD type memory card.

better yet would be to read that into one of thse USB type memory sticks.

or even into a USB dongle that has a micro in it to read the memory and then send it to the PC for use in Excel or a database, or graphing software.

any idea ?

Dave

[batman]

Check Cubloc / under accessories - they have a very inexpensive SD card.
Cubloc CB2xx + SD card + RTC

You know you need to be a "host USB" to write to a USB memory.
Most USB hosts are PCs.

[Chip-Circuit]

Which is easier to get started with ? the CF card or the SD card ?

Dave

[max]

The commands are the same for both...
I personally like the CF better.

[Chip-Circuit]

technically, I like the SD better as it has fewer connections.

I am surprized that no one has posted the Sony memory stick specs. I would prefer to use that one for it's size and shape.

But, I think that sooner or later, someone will make the USB thumb drive a viable candidate.

I guess I'll see what I can find for cards and readers on e-bay before I buy one type or the other.

Dave

[bhecox]

With the lm34, the temp reading seems very unstable. between readings 1000ms apart the temp will range a whole degree and back again. Is this
common? I don't seem to see this with other micro processors. I am averaging the reading with Tadin(), Do I need to just deal with this with extra
filtering or am I doing something wrong?

[Travis_j_t]

I put a capacitor on it. It usually helps. Its mostly because the small voltage range that it works in. You could scale it or get a 12bit ADC.