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Hi folks,

I’m in the process of trying to up the bending game. I have been using a keenovo blanket for the last few years for both uke and guitar. I wanted to move back to a PID style controller so I picked up two of them from LMI. Two of them because I’m planning to bend the solid lining layers and the sides at the same time and want a blanket on top and bottom. That’s a topic for another day.

However, for fun, and because I had two controllers, I tested the temp at both the waist and lower bout. The lower bout temp displayed quite a bit higher throughout the whole heating process. The sensors were both placed between the blanket and top slat. No wood in there for this test, just the slats.

Is it normal to have two different temps in each zone and to have them be so far apart? I faintly recall a post about temp zones and best practices to place the sensor, but cannot seem to locate it.

Here is my setup:




Ideas are appreciated.

Brad


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I guess first I'd stick the thermocouple sensors right next to each other and see if they read the same. If they are showing the same temp, you can trust them. If not, swap thermocouples on the controllers and test. It could be they read differently and there may be a way to adjust that in the PIDs.

More likely however is that in the waist area, the clamping cauls are just sucking off heat like a heat sink and in the bout area there is less contact and less heat transfer away from the sensor.

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Brian R, Wood Mechanic
N8ZED

yes what is the wattage of the blanket I found the Keenovo were not very good. If you don't have 5 watts per square in you can loose a lot on thermal load.
The other thing is how the heating element in the unit is.

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John Hall
blues creek guitars
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Co President of ASIA
You Don't know what you don't know until you know it

The blankets are from LMI. Overall wattage is 1035 and sq in is 213 so that comes to 4.85 watts / sq in. That is if all you do is divide total wattage by area.

Do you mean the element integrated into the blanket?

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Did you go through the calibration process for the PID's? They can be off quite a bit until they've been calibrated to the particular blanket that you're using.

Dave

Good call, I will try that. I made the assumption it’s all from the same supplier so would work together. These controllers are marketed as being “intelligent”, which probably means they need to be trained first.


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Thermocouples vary in their response to heat. Even from the same source there will be variations.

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formerly known around here as burbank
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http://www.patfosterguitars.com

One thing to keep in mind is that what we are using as "bending blankets" are generally used as drum heaters - a way to keep chemicals in 55 gallon drums at an optimal temperature in an unheated warehouse environment. Having a uniform temperature from end to end of the blanket is less important than having the total BTU's output in a reasonably consistent manner. Overall I think they do a pretty good job, even for our unintended purpose.

I’ve done a lot of testing of monitoring methods using K-type thermocouples. It is important to know that the readings can vary among thermocouples, and the PID or temperature display can introduce its own bias, such that the same thermocouple can give different readings on different displays. And of course temperature will vary from point-to-point in your bending sandwich.

I tend to bend with 3 thermocouples and 2 displays. Having multiple readings helps to identify thermocouples that have gone “bad” (it happens). If your LMI controller has an Auber PID (at least the original ones did), there is a feature to increase or decrease the bias. You can find the detailed PID instructions on the Auber website.


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Clealy LMI is gone. Where Can I find similar?

You could make your own.

Building a PID-type blanket temperature controller
https://r.tapatalk.com/shareLink/topic? ... source=app


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Did you check the TCs in boiling water? Both TCs should read the same.
You could characterize the measurement errors and apply the error to the heat range you are working in by placing both TCs in room temp water, then into boiling water, for both controllers, plotting your results then extrapolating the line(s) out to your target temperature.

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Measure Twice,

Karl Borum

Tried swapping controllers? Easy enough to plug/unplug. Or trying a third thermocouple, and maybe number three agrees with number one or number two?

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Peter Havriluk

Argh. How about focussing on my question? The issue above was beat up a while back????

How about this:

https://www.ebay.com/itm/125256234823?i ... R-qimKK-Yw

I built mine using an "Inkbird" PID from Amazon (where do they get those names???) and a solid state relay, etc. pretty much like in Tim's link. Didn't cost much to build and works fine. I don't know if anyone is building this kind of thing commercially or not.

Dave

I have used the same LMI controllers and a Taylor kitchen thermometer since 2004. Primitive by today’s tech but they work well for me.

IMG_7449 by Terence Kennedy, on Flickr

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It's not what you don't know that hurts you, it's what you do know that's wrong.

What’s with the attitude? Your question had to do with alternatives to an LMI-made controller, right? You got more than one answer, including a step by step guide to building your own. Just go do it.


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never mind. I appologize