dgramenz (Customer) asked a question.
Hello,
I'm new to the forum and looking for some advice. I'm also pretty new to PLC's, so talk slow and use small words, please!
I'm working on an idea here. The picture below is of a position indicator on some grain handling equipment. When the gray crank at the bottom center of the picture is turned, it swings a distributor back and forth to divert grain to different bins. As the distributor turns, the pointer on the white dial moves to show the postion. From where the indicator is pointing now (Truck Loadout), it can move clockwise to the far left position (Sukup 48'). It can only swing back and forth in the lower 2/3 of the white circle and will never move beyond that to the upper part of the circle. I would like to have an indication on my HMI of which position the pointer is in and also use that to enable/disable certain equipment, based on which bin is selected. There is a small amount of wiggle to the pointer, even when the distributor has locked into position on a bin. Would an absolute encoder mounted on the pointer shaft be the way to go? This would used with a Productivity 3000 and a C-more panel. Like I said, I'm very new to programming and am open to any and all suggestions.
Thank you.
Since your pointer does not make an entire revolution, and stays within the 2/3rd of the dial, I would use a 5k potentiometer like this one:
https://www.automationdirect.com/adc/shopping/catalog/drives_-a-_soft_starters/ac_variable_frequency_drives_(vfd)/vfd_accessories/remote_keypad_-a-_accessories/gsda-5k
And connect it to an analog input module (4-20ma better if the pot's distance is long from the PLC) . You'll have to generate your scale (when pointer is in current position, pot reads X, when pointer is at "Sukup 48" the pot reads Y, etc.) to get your data points for the HMI.
Just my 2-cents.
I happen to have one of those exact pots sitting here, unused. I should have mentioned though that this is a very dusty environment and I'm not sure how to mount one of these to protect it. It may be an option, though.
I agree with Todd that a potentiometer seems like a simpler option if you already have an analog input module with a spare channel. However if you have to add a $261 (or more) module the calculation changes. Sure one of Automation direct's absolute encoders costs a bit more than that and requires a number of discrete inputs but I can image one already having some spare discrete inputs, (and an 8 point discrete input is less than $100 if needed) Plus the encoder is IP65 rated ("P65 Enclosure - IP rated as "dust tight" and protected against water projected from a nozzle.") which seem desirable for the application.
If one does use a potentiometer, one might consider something like a https://www.automationdirect.com/adc/shopping/catalog/pushbuttons_-z-_switches_-z-_indicators/22mm_metal/potentiometers/ecx2300-10k and put it in a sealed box, perhaps something like, https://www.automationdirect.com/adc/shopping/catalog/pushbuttons_-z-_switches_-z-_indicators/22mm_metal/22mm_pushbutton_enclosures/pbgx1
In that case; potentiometer + box + analog module is pretty close to encoder + discrete module in cost, so the choice is not all that clear.
One thing I noticed is that there are only 8 marked sectors on the dial, how much resolution do you really need? Depending on how handy one is with mechanical construction one might consider three cams and three sealed limit switches or proximity sensors (binary encoded for 8 possible positions or possibly four for 16 positions, one could do even more but it quickly becomes more practical to just buy an encoder) .
If this is a one off personal project one needs to consider the value of one's time, if a commercial product one would consider the volume. For example, if one needed 100 units, buying the encoders at retail form Automation Direct would be $29,400 (but of course one wouldn't do that) just as example, 300 https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/limit_switches/plastic_compact_limit_switches/metal_plunger_with_roller_actuator/aep2g12z11-1 would be $5100, a $24k difference. A fabrication shop with a laser cutter could most likely fabricate a hundred cam assemblies for significantly less that that. Then the question is, is it enough less to pay for engineering and bookkeeping and leave you far enough ahead to make it worth while (but remember procurement and mounting of the other options has costs too)
I do have 4 spare input channels and 4 spare output channels on an 8 In/4 Out combo module. I also have space for 27 more discrete inputs between two modules. I like the IP65 rating for the dust this will be subjected to.
I see what you're suggesting with the cams and limit switches. I don't feel like I have the space to do that. The area behind the dial is full of cables, pulley, chains, and sprockets. I don't want to expand out to the front any more than necessary for aesthetics and because this can be a somewhat high traffic walkway, where it could be an obstacle. This is also a one-time project for myself.
When you say resolution, I'm not really sure what I need there. You're correct that there are only 8 positions to read on the dial. So I'm assuming I only need something with a very low resolution?
Thanks
I'd agree with Tinker, A 4-20 device would work great if there's already a 4-20 card. Personally I'd prefer something like that or an encoder as the "slop/wiggle" is easily accounted for in programming and I hate adjusting limits/proxs. But those would be cheaper if you're bored.
Hi dgramenz,
+1 Todd Dice
There are several ways to accomplish what you want to do.
Can you be more specific on the actual hardware you have on our P3000 and C-More?
List any spare IO - digital or analog.
Regards,
Garry
https://accautomation.ca/series/productivity-1000-plc/
https://accautomation.ca/heres-a-quick-way-to-convert-grey-code-into-binary-for-plc/
https://accautomation.ca/series/c-more-hmi-series-panel/
I'll try to list what I can.
P3-550 CPU
P3-08TRS (8 point isolated relay output) - Full
P3-08TRS (8 point isolated relay output) - 2 spares
P3-08TRS (8 point isolated relay output) - 8 spares
P3-08TRS (8 point isolated relay output) - 8 spares
P3-8AD4DA-1 (8In/4Out 4-20mA analog combo module) - 4 spare inputs, 4 spare outputs
P3-16ND3 (16 point discrete input module) - Full
P3-16ND3 (16 point discrete input module) - 11 spares
P3-16ND3 (16 point discrete input module) - 16 spares
The C-more is an EA9-T15CL-R
Thanks
I like the absolute encoder idea as well. A pot is nice and simple, but this is an outdoor environment it looks like and dust was mentioned. I think an absolute encoder is better suited.
All AD absolute encoders look to be the same price, but you dont need high resolution and using a higher res one means more inputs used for now reason. So I would go with a 180 count model:
https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/rotary_encoders/medium_duty_absolute_encoders_(gray_code)/trd-na180nwd
That doesn't use too many inputs and divides nicely in 360 degrees so it is easy to use. In Productivity, you would just wire it up to the inputs, mark the tags for those inputs, and then drag over an absolute encoder instruction. Set the tags in it and you are basically ready to go for using it. Just manually turn your handle and record what values are what positions and write a few lines of code to turn on different bits or even write a string for the HMI when the value is at different ranges. that correspond to your real-world positioning.
I also like the Absolute Encoder.. I'd Belt drive it off to the side.. Have the Encoder Shaf facing toward you in this picture.. this way you can use the Angle Bracket to mount the encoder. Then toss on some Toothed Belts and Pulleys, and you are good to go.. Does not have to be a 1:1 ratio, as it never turns one rev..
Cap
+1 Cap.
This is first step then add a motor and gear box and automated this. Sorry thinking out loud.