There’s a reason why you ought to do a measurement system analysis before you take measurements. For example, I didn’t sleep a wink last night due to my measurement system and how badly it had screwed me up.
My home energy usage has been a favorite target of mine for optimizing. Why? No, it’s not because I’m particularly environmentally conscious. Yes, I recycle everything that’s recyclable. I’m certainly not the worst offender out there, but I’m no Ed Bagely Jr. either. However, with the rapidly rising oil prices over the past year (despite the sudden decline), I decided it was worth investing in my furnace. I had a new tekmar 260 boiler control and indirect fired water heater installed over the summer. Based on my calculations, the expense has between a 2-4 year ROI. And there’s some feel good value from burning less oil.
All summer I waited, giddily practically, to see how the new system would perform once the heating season came. Then, late September came and I finally was about to get to see the benefits of the change. I’d been waiting for some time to pass so I could go down to my basement and get the first rough reading of my oil use, which I tried to do yesterday.
That’s where the problem with my measurement system started. I don’t think there are many people out there who are as obsessive as I am about data. Certainly, most people just want to know approximately how much oil is left in their oil tank. As a result, most oil tank gauges, including mine, are pretty basic. It’s essentially a float and a little empty-1/4-1/2-3/4-full scale inside a 3 inch high cylinder. There’s nothing high tech about it.
Based on my data, I figured I should have about 3/4 of a tank of oil left. Imagine my surprise, and then pure panic, when I went down to the basement to look and saw I had a meager one quarter of a tank of oil left!!! I had just had 139 gallons added to the tank on September 3rd and just 266 degree days had elapsed since then. According to my calculations (yes, I have a regression formula for my oil use), I should have used just about 46 gallons of oil (about 20% of my tank)! Was there an oil leak? I didn’t smell oil. I didn’t see any patch of oil around the furnace or the tank, so that couldn’t be it.
Somehow I’d used almost 170 gallons of oil in just a month and a half! And thus, I didn’t sleep a wink. The last time I bought oil, it was $4.04 a gallon. I’m sure it’s gone down by now, but that’s almost $700 in oil!!! I really don’t want to spend $700 on nothing. Immediately, I reacted to what’s changed. My new furnace equipment! It must be wasting lots of oil. I’m have a full fledged fit now, tossing and turning in bed, running over and over in my head how I’m going to get the installer of my equipment to pay for their screw up. How dare they sell me equipment that made my oil use four times WORSE than what it was without the new equipment. I started to wonder if I knew a good lawyer.
A note to myself, and anyone else who’s obsessive like I am, don’t gather data that might make you unhappy if you can’t do anything about it until the morning. In the morning I phoned the furnace company. I explained to them my observations and asked if they’d send someone out. They said they’d never heard of anything like that and would call me back. I spend the morning pacing, calling back at 10am for an update.
They tell me that they’ve run the numbers and they don’t see any way my furnace could have burned that much oil in that time. I feel a little better, but not much. My oil gauge still says my tank is mostly empty. I go back down to the basement. I tap on the sides of the tank trying to listen for the change in tone where the oil level would be. It sounds hollow to me, an unsettling sign. I wonder if the gauge is working. I tap on the gauge, but it doesn’t budge. I start looking on-line for other ways to measure my oil use.
I call the furnace company back and ask them if there’s a way I can check if the gauge is working. They tell me that they don’t know of a way, but suggest I call my oil delivery company and see if they have any ideas. So I call them. The guy there tells me the gauge I described can be unscrewed and a thin measuring tape can be slid in the hole to measure the depth of the oil. Heartened that I now have something to do besides sit on my hands, I head back down to the basement with the tape measure in hand.
Upon reaching the oil tank I unscrew the clear plastic tube that the float gauge sits in. And no sooner than I have loosened it two or three turns, the float gauge bobs up. Ack! There’s nothing wrong at all, except that the float gauge was stuck inside the plastic tube and so couldn’t move. I’m half relieved and half embarrassed that I’d called all these people for help and there was nothing wrong at all.
Still, I finish unscrewing the gauge and then press down on the float a couple times to make sure it comes back up like it should. Sure enough, it does. When I put the plastic top back on, it now reads 3/4 full. I call both companies back, apologize for the inconvenience and thank them for helping me out.
So a simple mechanical failure (friction of the float on the gauge) and my own hyper focus on this measurement led to a miserable night and day for me and two very confused companies who couldn’t figure out how I’d burned that much oil in a month and a half. In retrospect, thank god I had not had people out for a service call to look at the problem. I would have been paying $65 or more an hour to have nothing wrong.
And that’s where my story collides with process improvement. Simple float gauges aren’t that accurate in the first place. The tank isn’t square (it’s more like an oval), so the gauge doesn’t accurately measure the contents of the tank anyway. A linear measurement doesn’t take into account that the first 1/4 of the tank in height holds substantially less oil than the 2nd and 3rd quarters. Secondly, my measurement system failed anyway. Being ridiculously simple, the gauge simply got stuck rubbing the inside of the plastic tube. If I’d just checked my measurement system the night before (and I suppose it would’ve helped if I knew that plastic tube unscrewed), I would’ve slept soundly and had a good day.
I’m feeling much better now, but doesn’t it make you wonder how often your measurement system had led you to take corrective actions when there were none to be taken? I’m not saying you can’t have some measurement system noise. After all, I would’ve been happy with any measurement between 3/4 full or more. I just had a rough idea of where the gauge should be. But when the noise outweighs the signal, like the noise of a stuck gauge no longer measures the oil in the tank, you can’t make decisions on it anymore. Well, you can make decisions – like to toss and turn and fret over the data and make unnecessary phone calls and potentially pay hefty fees for nothing at all. I’d just suggest learning from my mistake. Check your measurement system.
