use of ROL and SHFT(shift register)instruction

[priya 0]

Dear Friends, In one of our project one voltage transducer is used to measure voltage at 24 different points in one operation cycle and it displayed in MMI, in this i want know how one transducer used to measure the different points using ROL insturction. And also please explain ROL and shift register instruction with some example, its very useful to me. THANKING YOU AND REGARDS D.gandhi kumar

[panic mode 246]

homework eh? you need to look closer... PLC instructions and code are PLC internal , transducers are external. To do multiplexing of external elements (phisical circuitry) you would need external switching elements (such as relays) which would be controlled OR monitored by PLC. suggested use of ROL and SHIFT instruction indicates that PLC is controlling (not just monitoring) switching elements. you probably have something like this: - PLC controlling bunch of relays (PLC controlled "selector switch") - 24 input circuits wired to those relays - other side of the relay circuit ("common") is wired to transducer - transducer is wired to PLC analog input. Downside of the approach is speed and complexity: - one has to make sure the switching is complete and reading has settled before next point can be tested. - wiring mess is harder to troubleshoot - trouble with shielding (number of relays and their phisical size would make such circuit very susceptable to noise). when ever this (switching) has to be done, one looks for more compact solution since reducing phisical size of the circuit can help fight the noise and increase switching speed (use integrated circuit chip instead of bunch of relays) which is much more practical on PCB level design, not PLC... back to original question, one would use some type of logic that can control the switching elements. when ROL or SHFT instructions are to be used for such job, it is one output that is high at a time (out of 24 in your case). you may want to take a look at sequencing (samples in download section) using INC and DECO instruction as well. they all can do this job... but, it will take forever to explain every step of the project (wiring, programming, interface to HMI). you need to narrow the question down to a specific problem. for example you didn't even mention what PLC you have. examples of mitsubishi instructions are in the manuals (check download section). PS. it's better to use HMI since MMI is not politically correct...

[priya 0]

hello, Thank you for your reply. in download section where i get samples Thanking u, D.GANDHI KUMAR I AM USING MITSHIBUSHI PLC PLEASE GIVE SAMPLE PROGRAMME. TAHANK YOU, D.GANDHI KUMAR

[tragically1969 0]

Is he not asking how to take a reference from the voltage transducer (possibly connected to an analogue input) at 24 points and display this on the HMI ? I imagine they have got something moving about connected to the transducer which at certain points based on either inputs or time would take the sample from the transducer If so the SHFT (L or R) command would work perfectly, and i am not going to write it for him either ;-0

[panic mode 246]

1. Click on link Downloads on top of the window, 2. Click on Mitsubishi 3. Click on Sample Programs (or Manuals etc.)