Proper barograph linkage settings for maximum pen displacement?

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Hi. I wasn't sure where to post this. It does relate to Earth science, but still wasn't sure whether or not to post there. Anyway, I am trying to determine the proper settings of the linkage of my barograph so that the pen moves the greatest distance up or down on the chart with as minimal movement of the aneroid disc as possible (in other words, the most sensitivity).

I have placed some images here:



The second image down shows the configuration. A metal aneroid disc is attached to a rod that provides vertical displacement with changes in barometric pressure. The rod is then attached to a linkage system. The linkage can be adjusted to either magnify or demagnify the amplitude of the recording pen.

The arrows in the third image show movement throughout the system. The furthest left arrow is movement of the aneroid disc, and the furthest right arrow shows the aneroid rod attached to an adjustable linkage that also moves vertically. The top of the adjustable linkage is attached to an adjustable screw with locknut. Movement of this screw one direction or the other helps form the axle for movement of the recording pen on the chart. The curved arrows show axle movement one way or the other depending on whether barometric pressure is rising or falling.

Now my question is, what would the settings be for both the linkage and the screw so that the smallest change in the aneroid disc causes the largest change in the movement of the recording chart pen? Currently, I have the screw screwed all the way into the axle up to the locknut and I am utilizing the last hole in the linkage (top image). However, I am not sure this is correct.

Thanks in advance for your help.
 

Answers and Replies

  • #2
Tom.G
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The sensitivity is determined by the lengths of the various lever arms attached to the axle and their angles. These are the the arm to the pen and the arm connecting to what you are calling the 'linkage.'

The first way is to adjust the linkage so that the arm on the axle is closer to pointing to the arm from the aneroid diaphragm; in other words shorten the linkage. This of course is limited by how much the pen arm can be adjusted to keep the pen on the recording drum.

If you are up to some machining, or even some work with a file, the second way is to shorten the distance from the axle to the linkage.
You can do whichever of these is easier. Either:
  • Move the linkage attachment point on the arm closer to the axle,
  • Or machine (or file) the mating surface of the arm so the linkage attachment point is closer to the axle

Cheers,
Tom

p.s. What is the purpose of increasing the sensitivity?
 
  • #3
davenn
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p.s. What is the purpose of increasing the sensitivity?
Exactly !

Now my question is, what would the settings be for both the linkage and the screw so that the smallest change in the aneroid disc causes the largest change in the movement of the recording chart pen? Currently, I have the screw screwed all the way into the axle up to the locknut and I am utilizing the last hole in the linkage (top image). However, I am not sure this is correct.
is this not already a working system ?
if so, why would you want to mess with it and possibly/probably wreck it ?


Dave
 
  • #4
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Thanks to you both. I just shortened the linkage, so I'll soon see what that does. I picked the barograph up at an estate sale a few weeks ago, but its total amplitude is not matching the barometric pressure of the local weather station. It is showing rising and falling curves, but not to the degree of the weather station.

Before adjusting the linkage and screw with the locknut on the axle, I thought it might have been a pen pressure issue, but that turned out not to be the cause.

Someone pointed out that I might also have a partially defective aneroid capsule. I certainly hope not as that would probably exceed the cost of what I paid for the unit... even if I could still get a replacement capsule. The unit comes from the late 1930's and uses a manually wound up drum that is wound once weekly. At least the time appears to be spot on.
 
  • #5
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Since last replied, I've had the linkage as shown in the image, but the amplitude did not change and, according to the local weather station, it should have decreased from about 30 to 29.9. So, I have lengthened the linkage once again to the maximum and left the axle adjustment screw alone.

S6300218.JPG
 
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  • #6
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Been lucky enough to have a pressure drop within the last couple of hours. Since readjusting the linkage as shown, the line begins to show the decrease. Hard to tell yet, but I bet the amplitude still won't match the station's.

S6300223.JPG
 
  • #7
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As I suspected, although there has been a slight drop in barometric pressure indication, it still isn't matching the local weather station's. Mine dropped to 29.88 or so over the last three hours, while the station dropped to 29.81, so the amplitude of my barograph is still not matching. If there are any other linkage or screw positions that might work better (other than the above), please share. I was thinking of swapping out the axle screw for a longer one, but this will take some machining for the hole and bracket, so I am hoping for a better option.

Tom, you mention "Or machine (or file) the mating surface of the arm so the linkage attachment point is closer to the axle" but I'm not sure what that means. Do you mean removing the pen arm entirely (along with axle, etc), sanding or cutting the bottom and reattaching?
 
  • #8
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Given the age and possibly storage in a non-ideal environment, one thing to check before attempting major surgery is whether there is any corrosion, burrs, dried out lubricant, and/or dirt build-up at any of the pivot points, and sliding contact points in the mechanism.

If so, it may be necessary to carefully clean and polish such surfaces (possibly using a very fine Jeweler's rouge; I'd check around to learn what restoration experts have to say), relubricate sparingly with something along the lines of watchmaker's silicone oil, and reassemble. I can't imagine the aneroid develops much force, and every bit of it given up to friction reduces pen movement.
 
  • #9
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Asymptotic, thanks for the reminder. Although I thought I was confident that I had checked everything, I think I discovered the source of my errors today: the pen. I had slid it off of the arm a couple of weeks back to clean it, but when I reinstalled, I hadn't noticed until today that I didn't completely reattach it. It slides onto the arm in two spots, but I discovered that I missed one of the pen brackets. A slight wiggle and it moved all over the place. No wonder the curves weren't matching the weather station. Well, now installed correctly and no wiggles. Now the threaded screw and bracket are as they were in post 6, so I suppose I'll probably have to readjust but at least now I won't be working in the dark.
 
  • #10
Tom.G
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Tom, you mention "Or machine (or file) the mating surface of the arm so the linkage attachment point is closer to the axle" but I'm not sure what that means. Do you mean removing the pen arm entirely (along with axle, etc), sanding or cutting the bottom and reattaching?
That is not necessary. My suggestions were based on the first photos you posted which did not clearly show the adjustment screw for the link.

What is needed is to thread the adjustment screw further in to the axle to increase the pen travel.

Look at it this way:
  • For a given barometric pressure change the, aneroid capsule will move the linkage up or down a fixed amount
  • The top end of the linkage, since it is attached to the axle, will follow a semi-circular path around the axle
  • By moving the top of the linkage closer to the axle you are decreasing the circumference of that semi-circle
  • With that decreased circumference, the axle will have to rotate further to accomodate the same travel distance
  • This increases the mechanical 'gain' to the pen so the pen moves further for a given displacement of the aneroid capsule
So the adjustment screw is effectively the system 'Gain' to the pen.
The length of the linkage, i.e. which hole is used, is the 'Offset' or 'Zero' of the system.

Start with the Adjustment Screw at about the middle of its range.

See post #13 below. Further information from the OP made this procedure obsolete.
The Calibration Procedure would be:
  • When the local barometric pressure is close to the middle value on the graph paper, set the linkage length so the adjustment screw is parallel to the arm from the aneroid capsule
    • If the pen is far from the correct reading, the height of the aneroid capsule may need adjustment so the pen matches the local barometric pressure
    • If needed, adjust the four screws holding the aneroid capsule by equal amounts. This may require a different linkage length to keep the adjustment screw parallel to the arm from the aneroid capsule
  • When the pressure is significantly different from the center value on the graph paper, set the 'Gain' (adjust the adjustment screw) to get the same reading as the weather station
As these two adjustments interact, it will take several attempts to get it spot on.
You will probably only be able to get the calibration 'fairly close' to the real world.

You may find two adjacent holes in the linkage that are 'close' but give opposite calibration errors. If you want closer calibration you will have to make a fine height adjustment of the aneroid capsule with its four mounting screws. I recommend you pick a day when the local barometric pressure is near the center of the graph paper and adjust the capsule height to the correct reading.

Then repeat the above Calibration Procedure.


Hope this helps.

Cheers,
Tom

p.s. please keep us updated on your progress... or non-progress! :oldwink:
 
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  • #11
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Thanks for the more complete explanation, Tom. Up until this, it has been sort of difficult for me to understand how the entire system works. Also, you've told me more in these couple of posts that I found with repeated web searching. I was able to find a few manuals on barographs, but nothing going into more detailed calibration procedures, at least nothing beyond setting the pen position with the calibration screw.

I have now reset the bolt about halfway between the axle as last night's trace still wasn't correct. I figured that I'd have to start making adjustments since I had them far from where they were originally. Luckily, I do have a photo reference of where everything was before I started adjusting even though that wasn't correct either.

I just wanted to mention that the weight circled in the image below unscrews and allows full pen arm movement independent of the axle and linkage system.

S6300227.JPG


Finally, in case it has to be adjusted, I wanted to be clear on which aneroid screws to adjust. There appear to be two screws securing it to the wooden base circled in red below. I'm not sure whether or not the screw holding the linkage and arm is another that would have to be removed or not. Then there are the other two screws I've circled in blue. I read somewhere that these were supposed to never be adjusted? Just wanted to clarify. I hope I don't have to go to this step, but just wanted to be certain if I did. Thanks for all your help and clarification.
S6300231.JPG
 
  • #12
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Hi Tom,

Please ignore post #11 above. I tried to edit so I could clarify, but I didn't see a way to. Anyway, thanks for your helpful responses so far, especially detailing calibration. I've read your instructions, but I do have some remaining questions that I'm hoping you can address. Please refer to the image below. These are all areas of uncertainty as I'm not sure how they figure into calibration (in other words, not sure how to adjust):

S6300237.jpg




The violet circled screws are the two bolts that bolt the capsule to the wooden base (top right inset image). You can see the screws more closely in the two bottom center and bottom right inset images also (not circled however). In addition, there is a bolt to the right of "Taylor" (see post 11 above) that I believe also passes through the metal base into the wood. Then there are also two screws attached to the metal plate that attaches to the center of the aneroid. These are circled in green, and there is a close up in the bottom center inset image. I'm wondering which of these five screws would need adjusment in the event the capsule had to be moved closer to the axle? I read that the screws attached to the plate are not supposed to be touched, but just wanted to make sure.

The bottom right inset image is the pen adjustment bolt (circled in blue). Where should I adjust this (and therefore the capsule distance from the base (shown as the large yellow oval) before I begin calibration? Right now, as you can see, I've tried to have the capsule approximately equidistant above the base which equates to about 40% of the total bolt length (bottom right inset blue circle).

Another thing I'm wondering about is the arm, and where it should be placed in relation to the adjustable axle bolt. The arm weight, bottom left circled in red, can be loosened and the pen arm can then move independently of the axle. I've already adjusted this prior. Is there any special position where this should be?

Your clarification on these points would be welcome (sorry if it's confusing, I was going to simply revise my prior post but not able to).

Thanks again!

Jon
 
  • #13
Tom.G
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Ahh! More information.

First, Taylor is still in business but no longer shows a barograph as a product. You could try an email, including a photo, asking if there is ANY useage or calibration information available. http://taylor-enviro.com/taylor-support/
If you get the run-around from them, you could see if they have a Facebook or Twitter presence and politely ask there for information.

That top view photo on post #11 is quite informative, especially the Set Pen screw. They made it easy to fine-tune the pen center position with that. It also eliminates my comments in post #10 about adjusting the capsule height using the four mounting screws (Green & Violet in your post #11 photos), best leave them alone unless absolutely necessary. (I will update post #10 to reflect that)

The implementation of the Set Pen screw is still unclear. Does the thick black metal piece it is in pivot freely on the screws circled in Blue in post #11?

The following assumes that the Set Pen screw is set approximately correctly, and freely pivots the black metal piece.

You mentioned you are on the 32nd floor of a building. Be aware that barometric pressure is typically reported for Sea Level. If the 1st floor of the building is at Sea level, the 32nd floor would measure 10millibar lower due to altitude. There is a correction table for altitude on pg. 21 of this document:
https://www.starpath.com/downloads/Fischer_Barograph_Manual.pdf

Here is a somewhat simpler
Calibration Procedure
On a day the local barometric pressure is about in the middle of the graph paper.
  • Set the Adjustment Screw about to the middle of its range
  • Set the Linkage so the Adjustment Screw is parallel to the arm from the capsule
  • Loosen the Counterweight (circled in Red in post #12), set the pen to the local barometric pressure, tighten the counterweight
    • This would be a good time to check the activity of the Set Pen screw. It can be used for fine adjustment of the pen position
On a day the local pressure is far from the center of the graph paper
  • Adjust the Adjustment Screw for the correct pen position
End Calibration Procedure

As these adjustments will probably interact a bit, you will have to check to see if the results are satisfactory. However, skip the counterweight & pen adjustment if only small changes are needed. You can't count on that adjustment for fine control.

If you can not get the calibration even close to correct, you may have the wrong graph paper on the drum. See this sight for some more info:
https://www.metcheck.co.uk/blogs/barographs

Of course if you can get details from Taylor, follow their instructions.

The University of Rochester has an archive of Taylor documents dating back to 1851 when the company was founded. A PDF catalog listing of holdings is available at:
https://rbscp.lib.rochester.edu/files/finding-aids/pdf/D120.pdf

You may also find this one interesting, (esp. Part I, Ch.3) Guide to Meteorological Instruments and Methods of Observation:
https://www.weather.gov/media/epz/mesonet/CWOP-WMO8.pdf

Cheers,
Tom
 
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  • #14
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Hi Tom,

Not 32nd floor, I'm at sea level. The weather station I've been using is online and located about 5 mi away, also at sea level.

The revised calibration procedure you've written above is actually what I've been trying.

Just to be clear, the set pen screw moves the aneroid up or down, depending on which way it is turned, and also therefore the axle eventually leading to the pen. I'm seeing the aneroid moving up more on one side than the other I think because of the way the "green" screws are set (and I haven't touched).

Yesterday, I backed out the axle screw almost completed so only just enough remained on the other side for attachment of the linkage and allow rotation. At bedtime, I set the BP to the local weather station using the above procedure. However, just a short time ago, my BP read 29.83 while the station read 29.61. Seems like no matter what I've tried, I cannot get the rising and falling curves to match.

I've been wondering for a while if I've been using the wrong chart, but with the curves I've been getting, any such chart is going to have to have an expanded scale over the one I've been using, chart 82, 28-31" range. I was told it was a Taylor model 2314 barograph, but there's no ID plate, just the numbers 8960 under the drum cover, which I assumed was a serial number.

I'll try contacting Taylor and see what I can come up with. Contacted Taylor and told they don't keep documentation for instruments going that far back.

Thanks,
Jon
 
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  • #15
Tom.G
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I cannot get the rising and falling curves to match.
Well that's a bit unclear. Are you saying that:
  • After a change in barometric pressure and then a return to the original value, that the pen does not return to the same reading?
  • A pressure higher than nominal, followed by a pressure lower than nominal by the same amount, gives different readings from nominal?
Those are two different problems.
If both occur, go after the first one as it may also fix the second one.

The first is excess friction, from the pen pressure being too high on the paper, the mounting screws for the axle too tight, a rough spot between some moving parts, there is dirt or oil between some moving parts, or there is some looseness or binding between moving parts where when one part moves or tries to and the next one doesn't (often call 'slop' or 'play').

The second is probably a geometry problem, either the parallelism between the arm from the capsule and the adjustment (gain) screw, or perhaps the vertical pen movement is not parallel to the drum axis, causing different frictional drag depending on the pressure reading.

Cheers,
Tom
 
  • #16
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Hi Tom,

By the curves not matching, I'm referring to the barometric pressure curve drawn over some hours by my barograph not matching the values of the local weather station, over the same time period. My curve never seems to go as high or as low as the station's. A week ago, I moved the pen just far enough away from the drum that it wouldn't touch, then used a camera to take images of the pen over the BP chart reading every half hour for twelve hours, then compared to the local weather station. Even without the pen touching the drum, the same lagging curves existed when comparing mine with the station.

I was in touch with a restorer earlier this evening. He suggested to "try shortening the distance between the vertical rod and the horizontal axle shaft" which, I believe, you also said earlier if I'm not mistaken. So, this time, I've adjusted the capsule upward quite a bit using the pen screw, then shortening the linkage and keeping the axle screw parallel to the capsule rod. The pen was placed on the target pressure by loosening, placing on correct BP, and then retightening the weight. This is about the only positioning I haven't yet tried and just waiting to see how it works out. I waited until the BP was about halfway up the drum.

Jon
 
  • #17
Tom.G
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"try shortening the distance between the vertical rod and the horizontal axle shaft" which, I believe, you also said earlier if I'm not mistaken. So, this time, I've adjusted the capsule upward quite a bit using the pen screw, then shortening the linkage and keeping the axle screw parallel to the capsule rod.
I think you mis-interpreted the suggestion.
What both he and I suggested, it not quite the same words, was to use the adjustment screw to get the vertical linkage moved horizontally closer to the axle. Please try to undo the most recent change. Then use the Adjustment Screw to get the pen deflection readings to match the extremes of the local pressure. Re-read the Calibration Procedure in post #13, especially the last step.

Use the Adjustment Screw to shift the Linkage closer to the Axle per this sketch.
BarometerSketch.png

Cheers,
Tom
 
  • #18
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not matching the values of the local weather station, over the same time period.
Mismatching the local station isn't necessarily an error/failing; my barograph located in Longmont, CO tracks reports from Ft. Lupton more closely than those from the local (presumably) airport; i.e., local barometric pressure is a highly variable property.
 
  • #19
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Mismatching the local station isn't necessarily an error/failing; my barograph located in Longmont, CO tracks reports from Ft. Lupton more closely than those from the local (presumably) airport; i.e., local barometric pressure is a highly variable property.
I understand, but I have a standard aneroid barometer I have been keeping near the unit, and I also calibrated it at the same time as the barograph, to the local weather station. Even it shows the BP a lot more closely than the barograph. Today, for example, the station reports BP of 30.32 whereas the barograph showed 30.03 and the barometer 30.30. I can see where the BP might be off a bit, but not as much as mine is showing.
 
  • #20
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Ok, I'm going to try this another way. Obviously, I'm not getting very far trying the adjustments recommended so far. I'm losing patience, not with this group of kind people, and in fact the only folks who actually showed an interest in trying to help me, but with the time taken trying to tinker it back to normal. I only paid a few dollars for it anyway.

So, can someone tell me exactly (or show in a diagram preferably) how the forces and results of those forces act in the barograph? Where, preferably (what BP... why only halfway up the chart?), should the adjustable axle screw be parallel to the horizontal rod emanating from the aneroid capsule? Is there any way, short of placing the barograph in a pressure/ vacuum chamber (which I don't have), that I can quickly see the results of the pen's amplification (or not?) based on the various adjustments of the linkage, axle screw, etc?

I would have thought that manipulating the "pen adjustment" screw after such adjustments might show the displacement as it makes a vertical line on the chart, but I'm not so sure this method is showing correct results. I've earnestly been googling for this. Diagrams and write ups will mention how the linkages, variable screw, axle, etc amplify the system, but there isn't an explanation anywhere as to exactly how.

The restorer I was in touch with said "Basically the idea is like that of a see-saw, where the adjust the amount of movement but changing the fulcrum." I'm unclear what that means.

I'm attaching an image I took of my barograph. I've tried to best show the adjustable axle screw, linkage, and rod emanating from the aneroid capsule. If I could visualize exactly how this system works with all of the forces, directions of movement, and results when anything is changed, I might have a lot better luck trying to get this thing to work correctly.

Thanks in advance and for the great patience and kindness the group is showing here.


IMGP0235.jpg
 
  • #21
Tom.G
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Is there any way, short of placing the barograph in a pressure/ vacuum chamber (which I don't have), that I can quickly see the results of the pen's amplification (or not?) based on the various adjustments of the linkage, axle screw, etc?
Referring to the top-view photo in post #11, try placing a coin on top of the assembly that is on top of the aneroid capsule, the piece that the horizontal bar is attached to. I have no idea how much weight will actually be needed, the idea is enough weight to move the pen a recognizable distance, still on the chart, without doing any damage. You may have to use a fishing sinker, or maybe just a ball of Aluminium foil.

The above will simulate a change in barometric pressure that you have control of for experimenting with the adjustments. Adding the weight will simulate an increase in barometric pressure.

You will find that as the Adjustment Screw moves the Linkage toward and away from the Axle, the amount of pen movement will increase and decrease respectively. Another way of saying it is, that as the Adjustment Screw position is changed, the pen will move different distances when the fixed weight is added.

Since the weight simulates a specific change in barometric pressure, you can see that you can make the pen move more or less for a given pressure change. This addresses the problem of the pen showing less change than the local weather station is reporting.

Tip: Write down the pen position without the added weight and with the weight, then subtract the two. This tells you how sensitive the pen reading is to that weight change. Change the Adjustment Screw position, maybe by half its length, and again write down the numbers and subtract them. If the Linkage was moved closer to the Axle the 2nd result will be larger than the first one.

Hope this helps!

Cheers,
Tom
 
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  • #22
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Hi Tom,

Thanks for the weight idea! I will try that tomorrow.

I did do a sort of rough check tonight with surprising results. I was able to fit both the barograph and a standard aneroid barometer I have here into a vacuum bag. I then inflated the bag and applied pressure. To my surprise, both units deflected upward the same amount.

Once that test was completed, I then manually set both instruments to the same BP as the local weather station. I came back a few hours later to find that both instruments showed identical new pressures, but were off from the weather station by the same amount. Now I'm beginning to think that having just a single aneroid capsule is the reason the barograph (and barometer) sensitivities aren't matching the local weather station, the barometer of which would undoubtedly have many capsules and therefore more sensitivity. Anyway, this is just a theory. I am still going to add the weight tomorrow and see what happens.

Jon
 
  • #23
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  • #24
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Ok, so, after your suggestion about the weight Tom, I actually did some experimentation last night as I couldn't wait until today. The relationship between increased weight simulating increased pressure versus linkage and/or bolt adjustment did confirm greater amplitude when the linkage was closest to the axle.

I think my other experiment (placing both instruments into the bag and pressurizing, then adjusting both to the same BP as local weather station afterwards) was also quite revealing. I have come to the conclusion that, although both the barometer and barograph will show rising and falling curves, because they have single aneroid capsules, their sensitivity will never match that of the local weather station. I confirm this yet again today. After roughly eight hours since my last readings, the barograph showed an increase from 30.48 to 30.49, then back to 30.48, while the local weather station started at 30.6, rose to 30.69, then decreased back down to 30.6. The standard barometer I have here shows 30.48 as of a little while ago. I had the amplitude of my system set to the max after using the weight for adjustment last eve.

Someone pointed out before that mileage distances between weather stations can make a difference, yet I've been monitoring two weather stations within a 10 mi radius of me and both have showed nearly the same pressures all along. Everything is at sea level.

It would be interesting to try and come up with a chart for my barograph that is actually correct. I probably could make something using enough data over the next few days. Just have to wait and see how it goes and if I also have the spare time.

Thanks again for all the help, especially Tom, for pointing me in the right direction.

Jon
 
  • #25
Tom.G
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Maybe you can figure out a way to get you and the two barometers closer to a weather station while also accessing their reported pressure.

Even if you do not have portable Internet access, a cell phone to someone with Internet access could work.

Another possibility is if the history of the pressure is published you could take the barometers to the weather stations, note the time and reading, then compare with the history later.

Or... variations/combinations of the above.

Anyhow, you seem now able to at least match the readings of your two devices. I would call that at least 80% success! Congratulations.

Cheers,
Tom

p.s. Please keep us updated on any further results you have.
 

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