I am continuing in my tests. As, you suggested I pass to the DAC 1000.
In the following table you have the results of what happens at ICs ouputs when the power loop is ON and OFF.
It is clear to me that the offset at pin 1 of DAC remains and you can see that there is a problem with the 5V when the power loop is ON.
I have a question concerning the connections on the board: the pin 8 of XTR115 (Vreg) is connected to pin 5 of R1SE-0505 (+Vin), is it correct?
I mean…the pin 8 of XTR115 is an output not an input: I don’t explain the connection.
It should be possible that my offset problem comes from it?
I am really stuck in the measurements. Is this a board that works properly?
pin 8 of XTR is an input pint.
Vref is an voltage output and on this board its left floating.
when you add the external power it increase the voltage on Vcc from 5.096V to 5.425V and this voltage is also used as a verf voltage by the MCP4725 ( MCP4725 usages Vcc as Vref). once the vref changes it will off set the dac value as well. when the vref is 5.096V the dac value will go from 0-5.096V but once the power loop value supply is one. this value will got from 0-5.425V.
You could account this offset value in the software.
could you explain how this off set value is changing the results, i might be able to suggest a solution.
Thank you for the explanation.
Now I can understand what happens, I mean…if I send 1000 to DAC the Vout will be as follows:
Vout= 1000*5.094/4095=1.244V (Power loop Off)
Vout= 100*5.496/4095 = 1.3442 (Power loop On)
If I want to change the value I pass to the DAC, for example 1500.
I measure the correspondent Vout at DAC (1.866V) only after switching Off and then On the external power loop supply.
In this way, It will impossible for me monitor any variations on the signal I pass to the DAC in real-time.
the change in reference voltage will change the scale but it wont affect the 4-20mA output. the 4-20mA range starts around DAC 290 and end around 1500.
once the loop supply is ON the reference voltage will be constant and the variation in 4-20mA will change accordingly.
Thanks, I completely understand.
It is still not clear for me why a variation on the input of the DAC doesn’t effect immediately the the output, I can observe the effect only after switching OFF and then ON the power loop. This is strange for me.
