does it matter that tekmar sensor is so far off?

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Old 01-15-09, 06:55 PM
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does it matter that tekmar sensor is so far off?

I have an outdoor thermometer that says it's 18, the internet says it's 16 but the tekmar says it's 24. My guess is it's definitely below 20.

comfort in the house is fine at 67 but I'm wondering if this is making my system any less or even more efficient? Earlier when the 260 said it was 26 out, the target boiler temp was about 158 if that matters or helps you decide.

My unprofessional guess is if im comfortable how things are now, it's no biggie if the sensor is reading too hot because if the sensor read the real temp of under 20 degrees, the water would be unnecessarily hotter.

Yes or no?

tekmar settings are 130 min 170 max with auto diff
 
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Old 01-16-09, 07:05 AM
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If it ain't broke (your comfort, that is), don't fix it.

In practice, it doesn't matter as long as the behavior of the sensor is more or less linear and consistent, i.e., it says it's colder when it's colder, and warmer when it's warmer.

The 071 sensor doesn't really have a spec for accuracy. It's supposed to have 10k ohms resistance at 25C +/- 0.2 C outdoors. Beyond that, it can wander. They are not highly-engineered. Just a cheapie resistor in a plastic box. But given the above requirement to simply tell the control when it is warmer vs. when it is colder and be repeatable, a fair amount of slop is ok.

FWIW, mine is pretty linear and accurate from 4-19F, and 25-75F. But it has a "higher than observed" bump of about 3F over the range 19-25F where it reads higher than two high-quality thermometers (one resistance, one mercury) nearby.
 
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Old 01-16-09, 07:14 AM
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Ok i'm glad for once what's "wrong" doesnt really matter (wish i could say that about my squealing bearing but thankfully i havent heard it in a few days) This morning the car said it was 9 out, my remote thermometer said 13 and the tekmar said 19. I guess i can always look there and think i'm 'warmer' than i am vs the frozen i should be

i never though of using the mercury one..i know where it is and may have to put it outside next to the sensor just for the fun of it! I'm assuming mercury is most accurate

Actually it was too hot in my bathroom this morning. was 69 in there! But the boiler is 66 all night and at 5 am i kick up to 67 so it runs for 1 hr and heats up that tiny space quickly and too warm sometimes i think. Out of habit i plugged in the cube heater as well and by time got done with shower was almost 72. ouch
 
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Old 01-17-09, 06:24 AM
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I have an additional tekmar question so rather than start a new thread, put it here.

I've personally witnessed many cycles of what a differential is, so am confident of what i've seen. For example if i have a target temp of 140 and the diff is 10, it will heat up to 150 and wait until 130 to turn on again. I've also, since turning it to auto a few weeks ago, witnessed the same exact thing. it shoots up the same amount it lets it cool down

So this perplexes me. the sensor says its 13 out, i'm cooking at target temp of 163 right now. I watched the temp fall to 147 and turn back on. Then when it gets to 163, it turns off!!!! Why isnt it going at least to the max setting of 170?

I hate mysteries.
 
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Old 01-17-09, 07:08 AM
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I hate mysteries.
Somehow Lucky, I don't think you do. If that were true, you wouldn't sit there and watch the boiler operate. You'd fugeddaboudit and grab a beer and watch the game!

There's two 'types' of differential... additive and subtractive.

High limit differentials are generally subtractive only, but without looking at the specs closely for your control, I can't tell you exactly what yours is.

Some are 'centered' around the setpoint, as you seem to think yours is based on your first example, but your second example clearly shows a subtractive diff. It can't be both...

Seems you've got more than a mystery! You've got an ambiguity!
 
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Old 01-17-09, 11:09 AM
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the 260 splits the diff if you set it manually....even my installer didnt know that but i did because i stare at the thing He was worried when it got X below the target and i said it's supposed to...sure enough he called tekmar and it does.

so if you manually set a 20 diff, it's 10 above and 20 below. Plain to see that in the manual.

now that i'm on auto..it does appear something has changed. Rest assured if i find what it is, ill let you know. And it does appear to be 'both'

the manual says this below..so i guess it is saying hey, dont heat above the target?

If the Auto Differential is selected, the 260 automatically determines
the best differential as the load changes. This setting is recommended
as it reduces potential short cycling during light loads

Fixed Differential
The boiler differential is divided around the BOIL TARGET temperature.
The contact will close when the supply water temperature is 1/2 of
the differential setting below the BOIL TARGET temperature, and will
open when the supply water temperature is 1/2 of the differential setting
above the BOIL TARGET temperature.
 
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Old 01-17-09, 06:53 PM
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Originally Posted by luckydriver View Post
Fixed Differential
The boiler differential is divided around the BOIL TARGET temperature.
The contact will close when the supply water temperature is 1/2 of
the differential setting below the BOIL TARGET temperature, and will
open when the supply water temperature is 1/2 of the differential setting
above the BOIL TARGET temperature.
This means that for a TARGET of 160, a DIFF of 20 will fire at 150, and stop at 170.

It takes a couple weeks for the control to dial in. The more you mess with it, the longer it takes.
 
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Old 01-18-09, 07:57 AM
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Originally Posted by xiphias View Post
This means that for a TARGET of 160, a DIFF of 20 will fire at 150, and stop at 170.

It takes a couple weeks for the control to dial in. The more you mess with it, the longer it takes.
trust me I know all that and i havent messed with in in weeks while it's been on auto. But why is there a difference on auto vs manual and why it didnt get above the target temp at all on auto, per my above example.
 
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Old 01-18-09, 02:15 PM
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Because it is "learning." (Actually, developing data on error magnitudes and corrections.) No kidding, it can take 6-8 weeks to settle in. Read the wikipedia page on PID controller to find out more how this style of control works.
 
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Old 01-19-09, 01:52 PM
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Lucky, to get a more accurate reading from the outdoor sensor, pull 12 to 18 inches of wire from inside into the outdoor box. Just loop it up in the box with the sensor. The main reason that the outdoor sensors read high is that the wire conducts heat from indoors out to the sensor.

Having 12" to 18" of wire in the box with the sensor reduces the heating affect.

Even though it will most likely learn in OK with the high sensor reading. I've always preferred sending correct information to control devices. Besides, it's nice to see the correct outdoor temperature when looking at the display.

Al.
 
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Old 04-22-09, 04:48 PM
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well now that the hot weather is here i've come into a shoulder season issue. yesterday was 69 out. But was in 30s in the morning. So chilly in the house. I wanted to turn on the heat but the afternoon sun made my tekmar sensor read 82!

i had to get my manual out to set the override temp to the mid 80s so that the boiler would turn on for heat. Glad i know how to read the manual because someone else may have called for a no heat call
 
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Old 04-22-09, 08:05 PM
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Why didn't you just open the windows?

If outdoor temp was 69, and the sensor was reading 82, it sounds as though you need to reposition the sensor to where it will read more accurately!
 
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Old 04-23-09, 06:00 AM
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it was a 'cold' 69 lol....but i know what you mean...i do wish it was elsewhere but except for this shoulder season, i'm happy with the performance and probably will let it sit. The reason being that this will help me use even less oil! If the sensor being in the wrong place made me use more oil, i'd be really mad and id definitley move it

See, some asked me if this is reading wrong now, they guessed i must have suffered all winter. And i said actually no, i lowered things to 65 inside overnight and am very happy with 66 for occupied times. So the sun must not have affected it in winter that much.

and moving the sensor would be very difficult...a long way in my crawlspace to the back of it to feed wire and then putting it somewhere on the north side of the house. Ill never get a house with a crawl again
 
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Old 04-23-09, 07:37 AM
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Does the sun shine on it? Is it mounted on a wall that the sun warms? Warm convective air currents passing by it?

There might be some things you can do to keep it where it is and improve it's accuracy... perhaps a 'radiation shield' ?

Maybe take a look at some of the hardware that's available for this purpose for use with those fancy 'weather stations' that they sell...

Radiation Shield

Might be some info you can use.
 
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Old 04-23-09, 09:00 AM
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The sensor may actually be quite accurate. I thought my sensor was out until I shot it with an IR gun. It just happened to be in a very sheltered area (as recommended) that lost heat much slower than the surrounding area.
 
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Old 04-24-09, 06:55 AM
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yes after 3pm about the sun will be right on it for a few hours..it's in a southwestern 'interior' corner of my house. I do have a big cherry tree there but i guess it doesnt block the sun until later on.

I may consider the radiation shield if it bugs me too much. But since (unless you tell me otherwise) there's a 100% chance this will use less oil, not more, as a result of a hot sensor, i may just let it slide. Now if this could hurt my efficiency, id like to know that.


and well yes, the sensor 'is' accurate from the perspective of the sun shining on it But no way is there a legit 13 degree difference between the sensor, my North facing wired thermometer, weatherbug, and the action news team. They all said around 70 that day, nowhere near 82.

for the fun of it, it will be getting into the 80s and 90s this weekend so ill be sure to check it out though
 
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Old 04-26-09, 01:07 PM
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Originally Posted by luckydriver View Post

for the fun of it, it will be getting into the 80s and 90s this weekend so ill be sure to check it out though
just an aside for the fun of it...thermometer on north side of house says 85, tekmar says 103

boy i'm glad i'm not out in the sun frying Beer 4U2
 
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Old 04-26-09, 03:55 PM
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And what would an IR temp gun show if you aimed it near the Tekmar sensor?
 
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Old 04-27-09, 05:00 AM
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Originally Posted by Who View Post
And what would an IR temp gun show if you aimed it near the Tekmar sensor?
wish i had the money for one Boy wish i could harness this solar juice and use that to cook the hot water all summer. Then id save tons of oil
 
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Old 04-27-09, 08:30 AM
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Maybe just stick a simple thermometer there instead. The sensor may be reading the temperature at the spot where it is located accurately although that spot may not be indicative of the general temperature outside.
 
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Old 04-27-09, 01:48 PM
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If that sensor, or even the area around it, receives any direct sunlight it will read several degrees higher than the ambient temperature. I have a digital indoor/outdoor thermometer with the probe located where it "sees" the morning sun. If it is sunny that thermometer will read as much as thirty or forty degrees higher than the standard alcohol (red fluid) thermometer mounted around the corner some twenty feet away.

Even radiation shields can heat up and then in turn radiate heat to the shielded thermometer.

I once was in charge of a building where the outside reset probe was located on a brick wall facing the morning sun. It was utterly insane how the system responded even during the winter if it was a clear morning. I finally had to do away with that outside temperature sensor and locate a new sensor on the roof near the air intake for the building. It still wasn't right but it was a whole lot better than the original.

Bottom line for you, if you are comfortable inside and it would be a great hardship to mount the outside temperature sensor where it would always be shielded from sunlight AND other sources of artificial heat then just live with it.
 
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Old 04-28-09, 04:43 AM
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Originally Posted by luckydriver View Post
Boy wish i could harness this solar juice and use that to cook the hot water all summer. Then id save tons of oil
Summer? Ha. It's way better than that. You get full solar for a good part spring and fall too. Here in southern New England, we are already seeing solar DHW tank temps >150F. Been on full solar hot water for about two weeks. Will be that way until mid- to late-October. We do about 75-80% of our annual hot water use with solar. In the heart of winter, the solar will raise the incoming 45F city water to about 90-100, which means the boiler is just topping it off the last 30F or so. Great system. Simple, too.

The federal tax credit for solar hot water is 30% of installed cost. Check incentives for your state at

DSIRE: DSIRE Home

There are also utility rebates available, most of which are listed at the dsire site.

Payback can be as short as 4-5 years depending on how much hot water you use and how you heat it.
 
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Old 04-28-09, 04:58 AM
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ill check that site then..sounds good! do you have pics of your solar setup? sounds like a bunch of additional piping and controls needed on top of what i already just got installed though

and i'm pretty single right now so dont use a lot of hot water so payback probably would be much longer.
 
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