Hello there..
i need to make a project for an industrial presure sensor that measures the presure with a 4-20mha , i want to read it with an arduino from analog pins and send the results.
The problem is that i wont be able to make RND in the place that this machine is located..
i want to make a Replication of 4-20mha in order to work it out in my office , my knowlegdes in electronics are novice to moderate..
i found some articles like
Use a Battery and a potantiometer. If the battery provides 9V, you'll need 450 Ohms for 20 mA, 2250 Ohms for 4 mA. Take a 2.5 or 2.2 kOhms Poti in series with a 390 Ohms resistor, and you'll be able to go savely through the full range.
original poster say that this worked..
the only problem is that i cant recognize the resistors values in order to gather the stuff
BZX84C6V2L is a zener diode. the Resistors R4 is 1Klohm , but what is the 21 beside it..
what is the R5 value? 275Ω?
I am assuming you have a stable 12V DC supply so a zener diode is unnecessary.
I have used preset potentiometers to enable precise adjustment of the 4mA to 20mA range (and to avoid non-standard resistors such as 1.21kΩ, 275Ω and 250Ω in the circuit you found).
The 10kΩ resistor is to protect the Arduino in case you disconnect the 5V supply before you disconnect the 12V supply for the current loop.
Set the presets initially to mid-travel, then adjust them iteratively until you get between 4mA and 20mA when you operate the potentiometer.
I am also assuming your loop provides current from a positive polarity to ground.
I have chosen a 200Ω resistor with the Arduino to make the mathematics easy. 4mA will give 0.8V and 20mA will give 4.0V.
A value of 1K21 is a value of 1.21K which is odd to say the least. A 1.2K is standard but the extra 10R is not ans what tolerance will that resistor have to be to make it a meaningful value?
Grumpy_Mike:
A value of 1K21 is a value of 1.21K which is odd to say the least. A 1.2K is standard but the extra 10R is not ans what tolerance will that resistor have to be to make it a meaningful value?
1210 is s a standard value in the E48 series and quite common for 1% tolerance resistors. Totally unnecessary for that circuit of course.
I think the strange resistor values in the OP were obtained by academic calculation. The calculation will have used an estimated base-emitter voltage and ignored tolerances of other components.
I am assuming you have a stable 12V DC supply so a zener diode is unnecessary.
I have used preset potentiometers to enable precise adjustment of the 4mA to 20mA range (and to avoid non-standard resistors such as 1.21kΩ, 275Ω and 250Ω in the circuit you found).
The 10kΩ resistor is to protect the Arduino in case you disconnect the 5V supply before you disconnect the 12V supply for the current loop.
Set the presets initially to mid-travel, then adjust them iteratively until you get between 4mA and 20mA when you operate the potentiometer.
I am also assuming your loop provides current from a positive polarity to ground.
I have chosen a 200Ω resistor with the Arduino to make the mathematics easy. 4mA will give 0.8V and 20mA will give 4.0V.
