Analog input voltage

[ecaits]

Dear Friends,

I have two-three silly question in my mind...

1. If I give more than 5V, say 10V to analog pin of ADC then what happen???

2. If I give negative voltage to analog pin of ADC then what will happen???

3. If I have 4-20mA output of sensor, can I use it as analog input??? OR First I need to convert 4-20mA to equivalent 0-5V??? If yes, How can I covert the same???

Thank you in advance,

 

[KlausST]

Hi,

1. If I give more than 5V, say 10V to analog pin of ADC then what happen???

there are thousands of ADCs.... some will smoke, some will work as desired..

2. If I give negative voltage to analog pin of ADC then what will happen???

same answer

3. If I have 4-20mA output of sensor, can I use it as analog input???

You can´t use a sensor as input.--

But surely you mean if you can connect the sensor to the ADC input.. --> Yes.

I need to convert 4-20mA to equivalent 0-5V?

There are very difficult electronic devices that convert current to voltage ;-) their name is "R"

And in case if you want to ask what value to use: Just use ohm´s law with U = 4V and I = 20mA.
Why 4V instead of 5V: because with a standard ADC 5V input with 5V range you will get overflow.
Why not take care of 4mA: it is more simple to correct this offset in software...

Klaus

 

[Gorgon]

If you have more than one input/ unit connected to the same 4-20mA loop you should be aware that there is an overal limit for the voltage headroom on the loop. You should also be aware of the possible problems you may have if your input is not floating in respect to the other units on the loop, if supplied from the same power supply.

If you use a 2-wire passive sensor you also need to supply power to the loop.