PC based control system components:
1-Measuring devices ( tempreture – Pressure – flow .. )
These measuring devices should “transmitte” electrical signal in proportional to the measuring values.
Standard : 0-10 volt , 4-20 mA ...etc ( those called Analoge inputs)
And you may simply want to know the “state”not the "value" of something
Examples:
Does the bottle here or not ?
Does the tempreture exceeds 50 degree or not .. generally a binary choice ( those called digital inputs)
2- How does the computer understand these electrical signals ?
Actually you have two major alternatives :
A- Using Data acquisition plug in cards. ( Visit
www.ni.com and
www.adlink.com )
B- Using Remote terminal units that speak with the computer through comport (serial) (visit
www.advantec.com and adlink’s site)
Note: In many times you will have to “Condition the signal” to meet your hardware specs.
3- Now the computer get the data , How can you use it (analysis – storing – visulaizing .. etc)
You will have to use a software for this and you have here to alternatives:
A-Ready made software.
B-Develop your own ( my fave ) using a high level programmong language (e.g visual basic 6 , LabVIEW )
4-The computer will take some actions according to data measured (as you programmed it) and it will use the same devices that mentioned in the point number 2 and the output is also standard (0-10 v) , (4-20mA).. etc which called analoge outputs and also digital outputs
5- Finally, these electical signals will be applied to a “Final control element” such as an on/off valve , contactor to run a motor .. (digital outputs)
and the analoge outputs for sending set points , controlling an actuator ...etc
I hope i could helped you ..
Ayman Metwally