Afternoon,I've been researching 4-20mA inputs and PMW to 0-10v analog outputting and i just wanted to run it by the fine people of this board first to check I've not made any silly mistakes.Firstly, 4-20mA; A Temperature and Humidity sensor, four wires:Temperature +Temperature -Humidity +Humidity -Simple 250 ohm precision resisters in parallel with the sensors between the ground and the 12v supply i'm using.Output; 0-5 PWM to 0-10V analog:Simple RC filter to smooth the PWM then using a Op-Amp with a gain of two to double the output voltage.fPWM = 488HzDuty step = 0% -> 99.9%PWM voltage = 0v -> 5vR=51kC=1uFTransfer FunctionG_((s))=20/(s+20)Cut off frequencyFc=3.12HzFinal Vout value (without ripple)G(inf) = 4.995vPeak-to-Peak ripple voltageVpk-pk = 0.05vSettling timeTr = 0.117 sec
Simple 250 ohm precision resisters in parallel series with the sensors between the ground and the 12v supply i'm using.
The polarity symbols you have drawn for the round temp and RH are backwards.
Quote from: retrolefty on Feb 13, 2013, 04:45 pmThe polarity symbols you have drawn for the round temp and RH are backwards.Ah, that's not actually true, since the sensor is drawn as a current-source, and the signs represent currentmeasurement direction, not voltage. Usually the signs aren't written as the arrow serves to indicatepolarity.
I've no idea what, if anything, is the symbol for a 4-20mA sensor. A current source makes sense in my head at least.I guess if it was drawn correctly the + and - wouldn't actually be around it at all, the diagram only needs to show the 12V source and ground.The documentation however only gives the electrical connections in terms of a + and - so it's good to have for reference.In other news, 250ohm resisters ordered, I was shocked at how they start at £5 for such a tiny component. 0.1% tolerance and a specific use market do that i guess.