# How does Kenmore Smartwash dishwasher 'know' the load size and how dirty?



## Ultrarunner2017 (Oct 1, 2008)

Hey guys;
I've been curious about this since the Kenmore Elite dishwasher with smartwash was installed a few years ago.
When we set it to the Smartwash cycle, it goes through a sort of 'testing' phase where the time will change rapidly, or there will be dashes on the display. Then finally it settles on about 2:40. While running, the machine will do a lot of starting and stopping - especially in the beginning of the cycle. Then it runs pretty much continuously, switching between wash and drain and fill.
When the display reaches about 0:30, it will most often suddenly jump to 0:16. I suppose it has detected that the last cycle is unnecessary.
So my question is how the machine detects the state of the load.
For how dirty it is, I suspect it senses the water circulating through its pump using photoelectric sensors.
How it detects the load, I cannot figure. I mean, how would it know how many dishes are loaded, unless it has another set of sensors. Or perhaps it senses the amount of time it takes for the water to return to the circulatory system after spraying it out? The more dishes, the longer it will take to drip back down??

We have a GE washer that also has a similar feature. It is called 'precise fill' and tests the load size by spinning it for a few seconds, then measuring the amount of time before the tub stops spinning. Law of physics says that the heavier the load, the longer it will take to stop spinning - provided it always starts at the same speed.
But the dishwasher doesn't have anything like that to determine load size...

your thoughts?
Thanks
Ultrarunner


----------



## azeotrope (Jun 3, 2015)

I thought it just had a single turbidity sensor in it to determine how dirty the water is. First rinse, check, provide result, drain, repeat process and update time with each check.


----------



## chandler48 (Jun 5, 2017)

I absolutely don't know, but it could be like a Thermos Bottle. It keeps hot things hot and cold things cold................How does it know???


----------



## Chris616 (Dec 31, 2019)

I read one theory that I’m somewhat dubious about (see the second post here). What he’s suggesting is that after the initial water fill the machine knows the temperature of the water in the sump. Then the dishwasher starts spraying that water around and if there are a lot of dishes (ie. a lot of mass) the temperature of the water in the sump will drop faster than if there are just a few dishes. There are a few things that would screw up such an algorithm for calculating the load size, though, such as if the dishes start off much colder or hotter than “normal room temperature” or if there are some high-mass cooking pots making up the load.

The other possibility is that this is just marketing hype. A cloudy result from the turbidity sensor implies that there is either a larger number of lightly soiled dishes or a smaller number of heavily soiled dishes. A marketing person might then say that this one sensor judges both the size of the load and how dirty the dishes are.

Here is an interesting recent Master’s degree thesis comparing the energy and lifecycle costs of using a dishwasher vs manually cleaning dishes. The studies were supported by Whirlpool, which makes Kenmore dishwashers. The only thing that I read about smart sensors was:
“Sensor cycles (Auto Wash, Smart Wash, etc.) utilize optical waster indicators (OWI) that adjust water usage to the amount of soil in the load being washed. OWIs are turbidity meters that work by shining light through a sample of water in the tub, with the fraction of light transmitted through the sample being dependent on the amount of soil in the wash water [27]. OWIs take measurements throughout the cycle to adjust operation.”

Chris


----------



## Ultrarunner2017 (Oct 1, 2008)

Thanks guys. I guess turbidity sensors are what I was thinking of when I used the term 'photoelectric sensors'. So far as the load size, I really have no idea, but your suggestions of temperature make sense. Whatever the method, I'm sure it's the least expensive option available. I don't think the designers would care whether or not the sensing algorithms are correct all the time. No one is going to complain, so long as the dishes get clean.
I also read that in order to save water and energy, the machines use less water and more efficient motors - which could result in lower water pressure through the sprayers. So they extend the wash cycle to get the dishes clean. It may not make sense that running the machine longer would result in an energy and water savings, but apparently they've figured out that it can. I do know that electric motors (pumps) have gotten a lot more efficient over the past 10 years.


----------



## azeotrope (Jun 3, 2015)

Ultrarunner2017 said:


> Thanks guys. I guess turbidity sensors are what I was thinking of when I used the term 'photoelectric sensors'. So far as the load size, I really have no idea, but your suggestions of temperature make sense. Whatever the method, I'm sure it's the least expensive option available. I don't think the designers would care whether or not the sensing algorithms are correct all the time. No one is going to complain, so long as the dishes get clean.
> I also read that in order to save water and energy, the machines use less water and more efficient motors - which could result in lower water pressure through the sprayers. So they extend the wash cycle to get the dishes clean. It may not make sense that running the machine longer would result in an energy and water savings, but apparently they've figured out that it can. I do know that electric motors (pumps) have gotten a lot more efficient over the past 10 years.


It’s to do with the amount of water used. If they run both pumps together then they need a deeper sump to supply both water circuits. If they run each pump individually then they can use a shallow sump = less water. 

Household HWT are set at around 130-140 DegF. Dishwashers need to heat that water to around 150 DegF for proper sanitization. That means if there is more water in the sump then it needs to heat more water to that temperature. Since it uses a smaller amount of water for both bottom and top cycles then it saves on the heating cost of that water and there fore is more energy efficient.

They can also use a smaller pump motor if they are supplying less jet nozzles. They can run the motor twice as long without using additional energy. They reduce the number of nozzles being used at one time by running top and bottom circuits separately. It takes longer to clean but they can boast about the energy savings of it and that is what sells these days. People don’t buy the low efficiency fast units, they get the high efficiency units (and typically find out they are slower after the purchase, but it was the high efficiency that attracted them). 

With high efficiency comes high cost to repair. They don’t market that part of it though...


----------



## CaptTom (Dec 31, 2017)

My dishwasher (Maytag) has a quirk which I think is related to this issue.

If I use a certain brand of detergent pods, it adds almost an hour to the cycle time. There's a point about 6-8 minutes into the cycle where it pauses and the display goes to an animated rotating oval. I think it's "sensing" how "dirty" the load is at that point, and adjusting accordingly. Apparently there are only two settings; "normal" and "add almost an hour." I suspect that the "add" mode is activated by suds when I use the "wrong" brand of pods. I know there is a photocell of some kind in the sump of the unit. I've found I can trick it by using the "quick wash" setting, which always takes the same amount of time and never pauses for sensing.


----------



## Ultrarunner2017 (Oct 1, 2008)

I never considered that a modern DW had separate cycles for top and bottom. I suppose that's the reason for the two step soap dispenser. On the Kenmore, you put soap in the bottom dispenser cup, then slide the top one over it, and add soap to it. The top dispenser doesn't hold nearly as much soap as the covered one does, so I guess that one is used for the top cycle.

To assist the machine in getting the dishes clean, I (we) always rinse the dishes prior to putting them into the DW. Some people think that's a waste, but I think that's what the manual tells you to do. It makes sense, since there will be less dirt in the water, thus less getting trapped by the filter, and perhaps shorter running time?
In a machine my family owned when I was a child, there was no filter. Instead, there was a 'macerater', which ground up the bits of food so they could go down the drain.


----------

