Micrologix 1500 and HSC

[rlmts]

I normally do diagnostics and modifications, and therefore rarely start from scratch! So... I may need some 'hand-holding' here...

Planning to use a 1764-28BXB Micrologix 1500, and part of it's job will be to monitor a simple single channel encoder giving a pulse frequency of approx 200HZ. (I need to double-check this, it may be a little higher)

It will need to count to a preset, then modify some registers, clear it's accumulated, load a new preset and be ready to start again.

Now, it appears that the 1500 has a built-in High Speed Counter, is this correct?

If so, what would be the procedure for setting it up?

(I have many more questions, but let's start here)

[Ken Roach]

The MicroLogix family all implement their onboard "High Speed Counter" function by having the first few DC inputs wired to a n onboard hardware counter. These inputs can be used as normal inputs, as "fast" (like pulse catching or interrupt) inputs or they can be inputs to the HSC function.

There is a chapter on the HSC instructions in the Instruction Set Reference, and a good Getting Started document in the RA Knowledgebase as Article ID # 17447.

[rlmts]

Just did a bit more looking! It appears the HSC instruction is not available for the ML1200 or ML1500 (only avail for ML1000)

So, at that low'ish frequency (200Hz) can it be done successfully by making use of the 'fast' inputs?

Will program interrupts be required?

[rlmts]

Thanks Ken, I'll check that out.
(You posted while I was preparing my last post)

[Ken Roach]

We sometimes get into abbreviations more than we should, I think.

"HSC" is often used as a generic abbreviation for High Speed Counter, and that's how I was using it.

The MicroLogix 1000's high speed counter function uses an instruction whose mnemonic is "HSC". There are also instructions related to the high speed counter function whose mnemonics are HSL, RAC, HSE, and HSD.

The MicroLogix 1100, 1200, and 1500 controllers use a high speed counter control file whose acronym and common name is "HSC". This high speed counter function also uses HSL and RAC instructions, but more of the functions of the counter are built into the HSC function file.

To be clear, since this seems to confuse a lot of people:

MicroLogix 1000 has one high speed counter function.
MicroLogix 1100 has one high speed counter function.
MicroLogix 1200 has one high speed counter function.
MicroLogix 1500 1764-LSP has one high speed counter function.
MicroLogix 1500 1764-LRP has two high speed counter functions.

I really like my hardcopy of the MicroLogix 1200/1500 Instruction Set Reference (1762-RM001). Sometimes I take it to a quiet place with a highlighter.

[rlmts]

Thanks Ken, very helpful.

I now have the Instruction Set Reference and going through the 'HSC' descriptions.

I also wanted to know that if I only use I:0/0 for the simple counter input, will I:0/1 etc be available as standard inputs? The book keeps telling me this...

"NOTE Inputs I1:0.0/0 through I1:0.0/7 are available for use as inputs to other functions regardless of the HSC being used. "

But it's still not clear to me?

Rich

[rlmts]

Where the manual says...

"NOTE Inputs I1:0.0/0 through I1:0.0/7 are available for use as inputs to other functions regardless of the HSC being used"

Does this mean that In 'Mode 0' I can use I:1/0 for the encoder pulses, and still use I:1/1 -> 3 as standard inputs?

I don't think I understand the Example charts on Page 5-17 of the Manual (1762-RM001) If I did I guess I could answer this question myself.

Rich.

[bernie_carlton]

I have used the high speed counters. I have used the terminals marked 'Not Used' for other purposes. I believe the note you cited means that, even though a pin is being used in a function it can also be used as a standard input in the ladder logic. Of course, if a terminal is being actively used in a particular HSC mode it probably means that it is too fast to be used reliably as a contact in the standard ladder.

As a note, be sure to adjust the electronic filtering. While offline - click on 'I/O Configuration', click on the CPU, click 'Adv Config', choose 'Embedded I/O Configuration' tab, check the 'input filter' timing. Again this can only be done offline then download to the CPU. If the filtering time is too high you will get to a frequency where counting stops. Too low and noise may trigger the counts.

[rlmts]

Originally Posted by bernie_carlton

I have used the high speed counters. I have used the terminals marked 'Not Used' for other purposes. I believe the note you cited means that, even though a pin is being used in a function it can also be used as a standard input in the ladder logic. Of course, if a terminal is being actively used in a particular HSC mode it probably means that it is too fast to be used reliably as a contact in the standard ladder.

Thanks Bernie, but are you saying that on the ML1500 I can use I:0/1 upwards for other standard logic (PBs L/S etc) even if I:0/0 is used for an encoder pulse train?

Are they saying that the other Inputs in the group for HSC:0 are still available for use as standard inputs? Or should I start my standard input list at I:0/4 and leave I:0/1, I:0/2 & I:0/3 not connected to anything?

Rich

[bernie_carlton]

Then inputs marked 'not used' in the table for a given mode are definately available for use as standard inputs. Note that the 'filter' setting I noted affect more than one input so you may wish to leave an input with a lowered filter time alone.

Now you're asking about standard practice. I do tend to leave the lower inputs free in the original layout when using these PLCs just for the future possiblility of needing additional high speed functions.

[rlmts]

Thanks Bernie,

Looking at the Advanced Configuration for the input filters, I should perhaps leave I:0/1 not used, as this is part of the first Filter Group.
(Shown as I0+I1) and start my normal inputs at I:0/2 as I have no plans to add further fast counting (famous last words!) due to this being a PLC upgrade from a Telemec TSX 17-20 to ML1500 with same plant functionality.

Rich.

Would you believe I have only just noticed the 'not used' headings in the examples!

[Bob A.]

Attention Ken Roach,

I'm feeling slighted as I stand here with a 1769-HSC in my hand! I was really looking forward to your explaination of it.

If I understand it correctly, it has two high speed inputs. That is, unless it has four, but on the other hand, it might only have three.

I guess if it was simple, anyone could make all this stuff work!

Best Regards,

Bob A.

[rlmts]

Hey Bob! Stop hijacking! <lol>

Seriously though... I would like one last word of encouragement from someone to support what I am now planning to do.
(I have included some Descriptions to give you a 'feel' for what I'm working with)

ML1500 For Crane Traverse/Hoist Control

I:0/0 = Single Channel Encoder Input (Simple Pulse-train)(400HZ max from Traverse Wheel)
I:0/1 = Currently FREE (Spare)
Fine tune input response filter to suit Encoder input.

I:0/2 = Proximity Switch Input (L/H Trav Motor Exact Stop, Traverse IN-Position)
I:0/3 = Proximity Switch Input (R/H Trav Motor Exact Stop, Traverse IN-Position)

I:0/4 -> = Standard PX inputs for hoist positions and special traverse positions (Load / Unload area PXs and O/T LS's)

I have still yet to decipher the Telemec TSX17 code fully (with their FC Fast Counter) such that I fully understand what's currently being done with it. (to simulate this in the ML1500)

See any glaring issues anyone?

Rich.

[Bob A.]

Hi Rich,

No more hijacking, I promise. I had a momentary lapse and decided to try to be a commedian! Consider me properly chastised for the unacceptable beheavior.

I won't pretend to recognise all the components that you cite, but rather I can recount the issues that I encountered in like efforts.

To begin, the large cranes in the steel mill traditionally had a mechanical line shaft from one side of the bridge to the other to connect the wheels together to even out the bridge travel for both acceleration and braking. In later versions, when AC took over, the line shafts began to depart and sometimes so did the sync of travel from one side of the bridge to the other so the crane could become cocked in the building.

I have seen cranes in long buildings that had infrared lasar distance measuring systems on each end of the bridge to measure the distance to the end of the building so that the independent motor control systems could square up the bridge in the building. This began around the mid 80s and not that it is involved in position control, it was an component in regard to safety and accuracy in the unmanned warehouse concept, becasue the lasers provide at least the gross component of the long axis position measurement. The fine component was sometimes from encoders that were periodically zeroed within a zone, but his scheme was often in error due to the likely hood of wheel slide caused by operators that were in a hurry. Automatic control could reduce this with controlled accel & decel. The better way was to have a target that could be hit with a laser sensor when the bridge was in line with a row in the long axis. The down side of this was that it reduced the flexibility on the floor layout and the fixed flags had to be relocated to take advantage of odd locations on the floor. This can be done with long lasers now.

As for bridge traverse, I have seen infrared used in this axis as well as cable driven rotary encoders and early on, the best was a rack and pinion system that was probably unpopular from the cost standpoint. I would use lasers in this application now. Wheel slip requires consideration in this axis since a hook hitting the top of a finished product will be very espensive.

The third axis is by far the easiest in that there are two stage absolute encoders available that can be attached to the drum which takes any counting errors out of the elevation.

In regard to the ML1500, I've seen them often, but not used one yet. My current activity has been centered on the CompactLogix platform, which also uses the 1769 I/O, and hense my joke about the HSC. I have one in an application that seems to have a mind of it's own in that it appears that I am dropping counts even at a very low input freq. I need to buckle down and tame it in the near future because I need for it to be working. I have used the VHSC in the PLC5 family for many years wtih flawless performance so my expectation is that this one will work as well.

So to review, in regard to your Traverse Wheel, consider wheel slip on the track. For the left hand / right hand prox, consider that their relationship may change if the bridge is long enough to become cocked.
And lastly, if the Telemec is a hoist encoder, I suggest that you investigate the two stage absolute encoders. They have seperate course & fine sections.

Feel free to try me at robert.applegate@comcast.net


Best Regards,

Bob A.

Note (Commercial Reference), I have written a number of applications in the ML1000 that may coincide with your crane application. Check out this link: http://www.americansensors.com/Sensors.aspx

If you scroll down, you will see a crane application, that he has added.

[rlmts]

That's ok Bob, I was only joking!

You are obviously well versed in this area of control technology, I am not! (Mainly fault-finding, modifications, and small projects)

The plan was for me to do a 'simple' conversion of existing ladder code (in a Telemec TSX17) to a Micrologix 1500.

The functionality, and the hardware is supposed to remain as-is.

So, the task, at first, seemed plausable/simple enough, then when I was given the existing docs/data it only consisted of an undocumented ladder print-out from the TSX, (which was found to have used the Grafcet method of sequence control, not directly translatable!) There were some electrical drawings (with lots of scribbles of devices put in and taken out) and... well.. well that was it really. No Operator Manual, no info on the HMI, no descriptions of any kind whatsoever.

So the route I went down was, at first, to try to understand the existing undocced print-out, in particular, the Fast Counter on board the TSX. Hence my other post...

http://www.plctalk.net/qanda/showthr...2&page=1&pp=15

In one of my earlier posts I said "Oh, dear! no replies, shall I shoot myself now!?" And not one person was kind enough to say yes, and put me out of my misery! <lol>

Rich