Stupid question ALERT

[rsdoran]

This is a refresher for me on analog, I am writing it to be sure I remember without having to look for the info in books etc.

Analog cards can (in most cases) use:
0 to 10v
-10 to 10v
0 to 5 or 1 to 5v
0 to 20ma or 4 to 20ma

This is the part I want to make sure is right.
10 bit card is 2^10 (2 to the 10th power)=1024
12 bit card is 2^12 (2 to the 12th power)=4096
16 bit card is 2^16 (2 to the 16th power)=65536

Using say a 12 bit card with a 0 to 10 volt input or output would require scaling those values:
0=0
1=409.6
2=819.2
etc
Obtained by dividing the max of 10v into 4096

Of course to obtain more precision you would use smaller factors like .1v or .5v, 2.7v ....ie with the 10v value you would use either 100 or 1000 as the divisor.

Overall does this cover the basics?

 

[ROBO]

That's how I would do it. You would have a resolution of 2.44mVolts.

 

[The Dark Knight]

Yes, that pretty much covers it.
As I understand it the 10bit/12 bit is the resolution

12 bit = 4096
so, max (32768-1 for us Series 90 folks) gives a 2.44 mV resolution

16 bit = 32768
so, max (32768-1 for us Series 90 folks) gives a .3 mV resolution

As far as scaling, you use the same method as I.

 

[Greg Gauper]

Keep in mind that some PLC types do make a distinction between a Unipolar input (i.e. 0-10v, 4-20mA, etc) and a Bipolar input (+/-10v, +/-5v, etc.) and will apply the number of bits across the full range.

For example, a 0-10V input configured as unipolar would have a 12-bit count range of 0-4095.

That same input if configured as a bipolar input might produce -2048 to 2047 counts over a -10V to +10V range.

The configuration may be via hardware jumpers or via software configuration.

Also, some PLC modules play games with their theoretical resolution (AB SLC NI8 Module comes to mind).

You can configure the module for a 16-bit output, but in reality the module has a true resolution of 20,000 counts over the input range and the virtual 16bit number while having a range of 0-65535, actually increments 3.2768 counts for every 'real' count and so would count in steps i.e. 0, 3, 6, 9, 13, 16, 19, 22, 26, etc.