How to keep the last current value in AI845?
I make the settings in the card in ISP to keep the current value
But when the signal is cut or go to over or under range it give us the minimum range of the signal and can't keep the last good value
Am using control module and use signalinreal in it
ISP control is executed only when there is a hardware defect in the module (look for ISP in help).
I assume it will not be activated from under/over range etc, as that are not defects in the module.
I could suggest you to look for RealInReal in the help, hope it will answer to your question.
Here is some example from the help:
"When the Error output is true, the value of Out depends on the settings of the ErrorMode interaction parameter.
Select Freeze, to keep present value of Out.
Select Predetermined to set Out to a predetermined value.
If Through is selected, Out is updated in the same way as if Error is false"
Source: CBM help
The problem is that simple electronics cannot tell the difference between a signal at 22mA that can equally be a signal fault or simply a mis calibrated flow transmitter reading maximum flow. The correct decision is always to select High or Low range.
If you want something else it must be programmed based on knowledge of the signal and process behavior. And this programming is very likely to make wrong decisions at some point. It is generally much better to use max/min signal values than some potentially wrong and random signal value from a few seconds / minutes ago. All sorts of horrible unintended consequences can happen if you "fake" signal inputs and do not display real data to either the PLC or the plant operators.
If you cannot live with the consequences of a signal error on a single input then you should consider redundant I/O and multiple voted inputs.