Analog Signals handling
I need to write and monitor an Analog signal.
I read that I can use the scaling functionality that is available within the hardware configuration of the AI module and saw that the inputs are of type RealIO which consists of: 1) Value 2) IOValue 3) Force 4) Parameter 5) Status
My first question: I saw that both Value and IOValue of type real, does that mean that I can use "Value" directly and it is already scaled using the min/max that I set inside Parameters? And what is the usage of IOValue? I read the description as "Value from I/O before forcing" is IOValue is the real value after scaling or "Value" is the one? and from where do I get the force value if I enabled Force bit and do I have any access to the integer value before scaling?
My second issue: I am trying to use SignalInReal Function block, is it possible to control the alarms setpoints/limits, if yes from where can I modify these values?
Voted best answer
Yes, scaling is done directly in the hardware configuration Properties Tab (for instance on S800 I/O hardware like AI810).
Mapping a structured RealIO datatype variable on to dedicated channel, gives you scaled values for properties Value & IOValue.
Value is the "released" property, when you force the I/O-channel, (IOValue will still be connected to the "outside").
There is no integer value ever presented, due to true DCS fashion; scaling is done once, in the hardware configuration, not concerned with in FB or ControlModules instances.
More to read about SignalInReal, below is from the manual:
SignalInReal has an analog input, of RealIO data type, with several supervision functions, such as alarm and event levels, and faceplates. SignalInReal has a first-order, low-pass filter built in. The input is intended to be connected to an analog input I/O variable. The signal output is of real data type (Function blocks) and ControlConnection (Control modules). It supervises signal errors.
It can handle over and under range mechanism. Refer to Analog Input and Output Signal Handling in the System 800xA, Control, AC 800M, Configuration (3BSE035980*) Manual.