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Use a terminating resistance of around 560 ohms , and use a dc ammeter to calibrate your 4-20mA loop for:
1. Line regulation : Vary the input voltage for a constant load and
2. Load Regulation : Vary the load for a constant input voltage.
Check the extremities of process measurement in both cases.
Hope it answered your question!
Besides their physical sizes (number of pins and program memory) there are also small differencies in the BASIC commands ..
However, I can't see any reason why the PICAXE-18X couldn't be used in this application ..
Just verify the names of inputs and outputs and you shoud be fine ..
The numbers you mentioned have been selected with the reference to 5V supply ..
PICAXE analoge inputs are referred to +V supply .. see picture below .. therefore you should use +5V as your power supply, and the best thing to do is to select 78L05 voltage regulator with the output voltage as close to 5V as possible, or employ adjustable regulator such as LM317(L) and adjust the voltage to 5.00V ..
I have this circuit running but with some problems.
It starts with 4.9mA and after the reset button is pressed goes up to 12.9mA and further to 21.0mA then back to 0mA and LED flashes.
The same situation repeats each time I press button.
Why it does not start from 4.9mA up to 21mA and back to 4.9mA and so on?
How can I calibrate current from 4.9-21 to 4-20mA?
In FREEZE, after the line:
if w3<70 ...
if w3<45 then tweakup
With these changes implemented, after initial 4mA (or so) - on power on - when you press the button PICAXE should start the cycle and the sinking current should rise to 12mA (or so), wait a while, and rise to 20mA (or so) and the fall down back to 4mA (or so), wait a while and continue the cycle ..
As far as calibration is concerned, w4 is responsible for the current levels:
w4=80 for 4mA
w4=244 for 12mA
w4=408 for 20mA
If these values do not match try to change them +/- as much as required ..
Thank you so much for your help.
I modified 2 of 3 of values and now I have 4mA, 12mA and 20mA.
After I press the start button the circuit start cycles and one cycle take about 40s.
IanP, once again thank you very much.
This project can be realized with any microcontroller, especially ones with ADC block and PWM module build-in ..
PICAXE has all of the above plus it is extremely easy to program (BASIC) ..
Try to find out if there is a distributor somewhere near you .. the list of international distributors is available at:
**broken link removed**