I had to look back but now I see it now after the TIL300, Il300 etc.( Your ten steps ahead of me) I tested the circuit in the data sheet for the 4-20ma driver and it did not work well at all. That is why I went with the AD694 it really works great and easy to configure. For isolation I use the TI ISO124 low cost simple and it works pretty well. You'll have to use the chokes to knockoff the ripple as it does generate about 5-10 mv from the dc to dc converter. The way I set it up is Prop, DAC converter, isolation amp, and then out to the MA driver. I'm sure their are better methods but this one was cost effective and had the precision I required. Or just use three of those H11L1's out of the Prop into the three wire of the SPI dac and then out to the 4-20 ma driver.
I must say I LOVE the jellybean suggestions by Phil and the simple elegant solutions offered by Tracy! Brilliant!
Given we want to have the 4-20 isolated because many folks will want to power it with their own Data Acquisition system (some have 32 VDC and many have 24 VDC but their system if 2000 feet away and their GROUND is frequently higher or lower than the GROUND at the actual device (sometimes it can be a DELTA of 8 VDC!)...
As such the user will want to either use the LOCAL 24 VDC that is "given" to the device that is tasked with outputting 4-20 mA to represent the parameter, say temperature, OR they will want to use THEIR power...
When we have a SINGLE DAC being driven from the Propeller that looks like this... http://www.screencast.com/t/MuKZd5nd0Idi
I am not sophisticated enough yet to be COMFORTABLE with driving the 4-20 with a PWM isolated on the digital side because I do not understand how it would compare with a 12 bit DAC as shown above... Any help there on a comparison??
Thanks a million guys!
Apologies if the images do not show. I put URL's from Screencast UNDER them if that will work...
ie Opto: TLP293-4{GB} + 2 x dmMOSFET BSP149H6906 => Sub $1.50 BOM
and needs a Calibrate pass once assembled. Drift may get < 1% here ?
Just an update on the Toshiba & Infineon 'improved vanilla' set above, I think a two point calibrate (at least) would be better - that catches any possible transfer offsets and can make code simpler anyway, as you extract a Zero set value.
You would connect to a 16-24b ADC (i2c,SPI) with good reference to calibrate.
Comments
Here is one from a pretty sharp FAE at Arrow in Las Vegas!
http://www.screencast.com/t/yCBsvsoc
I must say I LOVE the jellybean suggestions by Phil and the simple elegant solutions offered by Tracy! Brilliant!
Given we want to have the 4-20 isolated because many folks will want to power it with their own Data Acquisition system (some have 32 VDC and many have 24 VDC but their system if 2000 feet away and their GROUND is frequently higher or lower than the GROUND at the actual device (sometimes it can be a DELTA of 8 VDC!)...
As such the user will want to either use the LOCAL 24 VDC that is "given" to the device that is tasked with outputting 4-20 mA to represent the parameter, say temperature, OR they will want to use THEIR power...
When we have a SINGLE DAC being driven from the Propeller that looks like this...
http://www.screencast.com/t/MuKZd5nd0Idi
I am not sophisticated enough yet to be COMFORTABLE with driving the 4-20 with a PWM isolated on the digital side because I do not understand how it would compare with a 12 bit DAC as shown above... Any help there on a comparison??
Thanks a million guys!
Apologies if the images do not show. I put URL's from Screencast UNDER them if that will work...
Just an update on the Toshiba & Infineon 'improved vanilla' set above, I think a two point calibrate (at least) would be better - that catches any possible transfer offsets and can make code simpler anyway, as you extract a Zero set value.
You would connect to a 16-24b ADC (i2c,SPI) with good reference to calibrate.