Missing the connects

OK I am setting up a Mitsubishi FR-D700. They want it to do do 15 preset speeds. I just don't see the easy connection. I have the truth table but it just doesn't click of me. (Probably not enough sleep)

I need to setup the some digital outputs to do step the speed. here is the table.

I thought about doing an integer ans stepping through the numbers. I can step through them but it doesn't look pretty.

It took me a while to see what they were doing. Not intuitive at all. I will try to explain how I see it.

It sure looks like this the result of legacy. They started with L M H corresponding to speeds 3 2 1 (notice that speed 3 is actually 'low', your chart should have rows '1' and '4' swapped).

They wanted more speeds so they used logical combinations for the next speeds. LM was speed 4, LH speed 5 and so on.

Then at some point further along they wanted even more speeds, so they added an extra switch, X. This time however instead of continuing the pattern it changed. X is speed 8, XL is speed 9, XM is speed 10, but XH is speed 12 and XLM is speed 11. More like 'normal' binary counting.

Anyway this is more or less an academic point. You could just use the four inputs and control them like speed select bits, you just have to remember that when programming the speeds, 1 to 15 won't be in ascending ordering.

If you make RL bit0, RM bit1, RH bit 2, and REX bit 3 then all you have to do is put the right speeds in the right parameters. [edit: original example was screwed up].

You are correct not very intuitive. I'm driving now so when I get a good point I can stop I'll read the full post

I'm sure they have a reason for doing it this way, but I agree, it's still strange. I'm guessing most people only need a few speeds, so they assigned 1, 2, and 3 as speeds 1, 2, and 3, and 'reworked' the rest to accommodate 15 speeds.

Notice how 8 through 15 is 'correct' if you change your left column to read 4-2-1-8 vertically. If you only needed 8 speeds, you could wire it this way and use binary to choose speeds 8 through 15.

For 15 speeds, I don't see any useful pattern, so one fix is to just stick a bunch of comparisons and range compares on each output rung, and turn them on when your chosen speed calls for that output.

Or just overwrite to output word to correct the 7 'wrong' values:

MOVE chosen speed to output speed
(value is correct for 1, 2, 5, 7, 8, 10, 13, and 15)
IF chosen speed = 3, MOVE 4 to output speed
IF chosen speed = 4, MOVE 6 to output speed
IF chosen speed = 6, MOVE 3 to output speed
IF chosen speed = 9, MOVE 12 to output speed
IF chosen speed = 11, MOVE 14 to output speed
IF chosen speed = 12, MOVE 9 to output speed
IF chosen speed = 14, MOVE 11 to output speed

At the end of the scan, the 'output speed' word will match Mitsubishi's wacky pattern.

Either way is cumbersome though...



-Eric

I have it. I will just use a bit pattern in the PLC. I will setup the drive in a step speed. It steps might be 1,4,8,12,6,9,8,13. All I have to do is get that pattern and set the speed steps in the drive. Who cares if they don't really lineup with what the step number in the drive.

I had a mistake in my above example. It's a little more complicated because speeds 3 2 1 correspond to L M H (keep forgetting that one).

I've made another chart showing the four switches and what speeds they select.

So to make everything work if you set the speeds in the following order from lowest to highest speed. You would set 3, 2, 4, 1, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 in that order. Which corresponds to parameters 6, 5, 24, 4, 25, 26, 27, 232, 233, 234, 235, 236, 237, 238, and 239. Then all you have to do is use RH, RM, RL, and REX as binary select switches.

The next problem will be to document this odd arrangement so that Bubba doesn't try to 'fix' it by putting the 'correct' speeds in proper order.

Screw all that, just go analog and give them 38 different HMI adjustable speeds

Seriously though, I agree that it looks to have evolved from 3 speed to 8 speed to 15 speed and they didn't want to break what they'd already laid out...

Nice analysis by Timbert and Eric.

OkiePC said:

Screw all that, just go analog and give them 38 different HMI adjustable speeds

Seriously though, I agree that it looks to have evolved from 3 speed to 8 speed to 15 speed and they didn't want to break what they'd already laid out...

Nice analysis by Timbert and Eric.

Click to expand...

IF you understand where this came from you undersand how it became the train wreck displayed.

Originally on these drives you had 3 discrete inputs. These inputs could be programmed as Preset Speeds 1 thru 3. Then someone got the bright idea that you should have more than 3 and they came up with the "extended preset" speed function. This extended function gave you 4 more speeds. Then to get the other 7 they added another input.

As to how I would handle this problem, I would build a lookup table. You only have 15 unique numbers so it will probably take you longer to fire up your programming software than to build the table. Remember these "Presets" correspond to a parameter in the drive so you need to stay in order or someone will get real confused. I believe the 1 thru 15 at the top of the table corresponds to Preset Speed 1 thru 15 the rest of it is just gibberish. It doesn't follow any real numbering pattern. So if you want preset speed 9 then you will need to turn on 4 and 8. if you want preset speed 3 then you turn on 4.

If you are just wanting to step thru the speeds from 1 to 15 then do your steps and make it pull the correct combo from the look up table.