ThePEee

Hi to all, new to this forum. I have some projects to upgrade existing control systems from GE Fanuc 90/70 series controllers to Allen Bradley GuardLogix (or ControlLogix). The projects must be managed in phases, where through a portion of the project, the existing GE and new Allen Bradley controllers will need to co-exist, sharing each other's connected I/O and processor status for program operation. I've reviewed some options for a communication card that would reside in the Allen Bradley modular rack, but concerned that effort to use an Ethernet based TCP/IP protocol is impractical due to GE's proprietary Ethernet protocol of the time period (circa 1992 for these controllers). Modbus serial is a possibility, but wanted to exhaust Ethernet options first. I have a SCADA connection in place now, using OPC server connection to GE and Allen Bradley processors in the plant. I would like something more robust with distinct traffic between controllers. I am also open to using a dedicated PC with network cards and drivers to connect directly to PLCs, but would prefer a third party packaged system to avoid development time and OPC type connections. Anyone have any ideas or tested solutions for this particular application? I'm all ears! Thanks in advance.

From your post, you seem to be interested in determining an 'instantaneous' velocity. I've supplied the definition which holds the key to your question. Given you have no form of feedback that does not require sampled data (counts), a processor and module with inherent delays (scan, data transfer), and the asynchronous timing between calculations and real data value at that instant, you will never have a true instantaneous speed. You can cut your time slice for comparing position counts and as with integration, come closer to an approximation of instantaneous speed as delta T (time) approaches "zero". Capture your delta between positions for a smaller time slice. You will eventually start getting some poor approximations of instantaneous speed when your time slice gets smaller than the inherent delays within your system. Arguably, a truer form of instantaneous speed capture would be a tachometer (analog voltage back to your speedometer reference). Instantaneous velocity is the velocity of an object in motion at a specific point in time. This is determined similarly to average velocity, but we narrow the period of time so that it approaches zero. If an object has a standard velocity over a period of time, its average and instantaneous velocities may be the same.