# AB SLC5

R

#### ramu

I would like to know why in the SCP Instruction set, the scaling is different for the input i.e. for 4- 20 ma input the scaling is 3277 - 16384 where as for the output, 4 - 20 ma it is 6242 - 31208

A

#### Allen Nelson

The numbers you are referring to are not intrinsic to the SCP instruction, but to the SLC analog input and analog output modules.

The analog input modules are 14 bit (i.e., 0 to 16384), that read 0 to 20 mA. Thus 4mA = 16384 x(4/20) = 3277 and 20 mA = 16384 x(4/20) = 16384.

The analog output modules are 15 bit (i.e. 0 to 32768) that transmit 0 to 21 mA (yes, 21 (max output)). Thus 4mA = 32768 x (4/21) = 6242 and 20 mA = 32768 x (20/21) = 31208.

(I know, technically the AI is 15 bit with the 15th bit being a sign bit, and it reads -20 to +20 mA, but describing it as 14 bit made the above description a bit easier to follow, I think anyway)

Hope that clarifies things.

Allen Nelson
Real Enterprise Solutions

G

#### GMAN

> I would like to know why in the SCP Instruction set, the scaling is different for the input i.e. for 4- 20 ma input the scaling is 3277 - 16384 where as for the output, 4 - 20 ma it is 6242 - 31208

If you get out the manual for the card you are using you will find that the input card is really 0-20 MA. The 3277 is the offset for the first 4 MA. As for the output, I don't quite remember, I think that the same logic applies. I also hope for a day when AB makes an analog card that doesn't require a clove of garlic and religious personnel to make it work.

Later
GMAN out

PS. Don't ever do analog flex I/O on a SLC scanner, or you will be forced to discover the joys of the M files.