[Logix5000] Dividing by zero

[robo77]

add min flow

 

[nhatsen]

I guess it depends on what you call a good solution.

I think we're speaking about 2 different things here:

1. Multiplying by the inverse of a number: I applied this "trick" when memory was measured in bytes and I needed to save memory. However, that trick requires that you know the numbers (constants) beforehand:

flow (gpm) = flow (mgd) * .00069444

You can write this equation because you know that .00069444 = 1/1440.

2. OP wrote:

I divide a bunch of variables by total plant flow to work out pump speed.

So the equation is some_variables/flow. If flow is zero, you get a math error. I suppose that some_variables * (1/flow) will give an error when flow is zero.

Said that, I agree with others members that it's necessary to place a compare block before the calculation. I prefer GRT block (never use EQU or NEQ with real numbers, and I suppose that flow is a real).

Also, in the equation some_variables/flow, if some_variables is too high and flow is too low, the equation could throw an overflow error. That's something to take in account.

 

[defcon.klaxon]

Thanks for all the input guys, really appreciate it. I'm gonna try the bypass of the compute instruction if the flow is equal to 0 and set the value. Shouldn't be too hard, thanks for pointing me in the right direction.