Lucas,
You ask very good questions. I've worked with the T100MD series PLCs for a number of years. I can give you a answers to many of your questions.
- What is the maximum scan frequency of the ladder scan?
With the following single rung program running on a T100MD+1616:
Output1 Output1
----|\|------------------------(OUT)
Output 1 runs at 207Hz (4.84mS period). This implies that the scan speed is approximately 414Hz (2.42mS period). There is some jitter in the waveform, which suggests that the PLC CPU is handling some periodic interrupt. RTC or periodic timer is my guess.
If I have a single ladder, with a single ladder element tied to an input channel, how fast can I pulse the input and have the PLC catch the pulse?
I don't have a setup to measure this. My experience has been that input events that that run faster than about 15Hz with a 50% duty cycle tend to get lost. My guess on the input speed limitation has to do with the logic that the PLC uses to debounce inputs.
The PLC assumes that you have a bouncy (noisy) mechanical switch connected to the physical input to the PLC. I suspect that they do some nature of digital filtering that requires an input to be stable for some number of scan periods before the ladder logic "sees" the new input state.
The PLC has some specialized handling for a limited number of inputs for handling high speed external events. Think look at the documentation for high speed counters, quadrature encoders, and interrupt handling that invokes a TBASIC function based on an edge transition on a specific input pin.
The "F" Series PLCs are said to be significantly faster. They are based on a much newer microprocessor core. I suspect ARM9 or something similar.
- What sort of performance hit is expected with an linearly increasing ladder rung count? Say each ladder rung is uniform, and of the simple sort described above.
I duplicated the first rung and changed only the OUTPUT associated with each new rung, I got the following timings:
#Rungs Period mS
1 4.84
2 4.85
4 4.90
8 5.08
You can do the linear regression work, but for simple ladder logic, the big time hit is probably saving the input state for all physical inputs at the beginning of the scan and then updating all of the physical outputs at the end of the scan.
- What is the relative performance hit of implementing functionality in custom function BASIC versus ladder logic-triggered RELAYS? What is the performance hit involved with using logical BASIC conditionals versus implementing multiple ladder rungs? (By BASIC I'm referring to if/else if/then/else conditional logic blocks)
Ladder logic is significantly faster than BASIC for manipulating I/O (bit logic). I do not have a test case for this.
If I get into situations that have large computationally dense BASIC code, I often break it into smaller chunks spread across several scan cycles. There are many games that can be played to get the most out of these PLCs.
- Is there a location where I can find the operating specifications of the T100MD-2424? I'm looking for a datasheet with operational characteristics, more so than an "installation" or "operation" guide.
No.
Gary D.
