What beam scale are you using?

[amlevin]

I have a 10/10 and a Denver instruments Commercial electronic.

The 10/10 is dead nuts verified by the Denver Instruments electronic Commercial.

That means that either both are "dead nuts" or both are "dead wrong". Which is it? :

 

[sparker]

A customer of mine has both a tuned beam scale from me and a magnetic force restoration type digital scale (Sartorius) He weighed out 20 charges of Varget on the beam scale and cross checked them on the Sartorius. The SD for the 20 charges was .012 grains. This is smaller in mass than one kernel of Varget.

Personally, I have experienced that my scales are sensitive to a single kernel of IMR 8208. These are very small kernels. I use scales that because of their condition (ugly, beater) I couldn't sell to customers.

Scott Parker

 

[Sheldon N]

Great info, Scott. Makes me want to add one of your scales to the collection.

 

[AckleymanII]

10/10 here and 505, checked both with a Denver Instrument commercial electronic, they are both dead nuts. I don't need the 505.

 

[sparker]

Just let me know Sheldon. I can supply you with a great scale.

Scott

 

[SteveOak]

RCBS (Ohaus) 304. Bought it new in the 70's? (60's). Sometimes I see them for sale used (not made for quite some time).
I used it exclusively until I bought my first electronic scale 2 years ago. Now i use it to check the electronic one since it is unaffected by radio signals , florescent bulbs, cell phones etc.

I also use the 304, but I don't own an electronic scale. I love the 304.

I haven't yet been able to convince myself that electronic scales are not affected by electronic/electromagnetic interference.

I can be persuaded that my concerns are completely unwarranted, but I've never heard anyone address my worries.

Does anyone know of studies addressing this issue?

My specialization is protecting electronic equipment on commercial aircraft from electromagnetic interference. We refer to small stain gauges, the sort used in lower and modestly priced digital/electronic scales, as RF detectors or temperature sensors.

They are quite susceptible to changes in temperature and to electromagnetic interference.

I use a Scott Parker tuned RCBS 10-10 and am very pleased with it.

Handy link to Vishay white paper on Noise Control in Strain Gage Measurements http://www.vishaypg.com/docs/11051/tn501.pdf

 

[BigBlueandGoldie]

Scott, I've been wanting to buy an old Lyman to have you tune, is there anything that I need to look out for or can you fix just about any issue a scale might have besides obvious neglect?

 

[SHootSTraight22]

Yea, I'm with the above question.. I've been on EBay looking at all the different used scales, is their a certain one that's better than the other??? Is knive edges better than the rounded beam supports??

 

[dixieppc]

RCBS (Ohaus) 304. Bought it new in the 70's? (60's). Sometimes I see them for sale used (not made for quite some time).
I used it exclusively until I bought my first electronic scale 2 years ago. Now i use it to check the electronic one since it is unaffected by radio signals , florescent bulbs, cell phones etc.

I also use the 304, but I don't own an electronic scale. I love the 304.

I haven't yet been able to convince myself that electronic scales are not affected by electronic/electromagnetic interference.

I can be persuaded that my concerns are completely unwarranted, but I've never heard anyone address my worries.

Does anyone know of studies addressing this issue?

My specialization is protecting electronic equipment on commercial aircraft from electromagnetic interference. We refer to small stain gauges, the sort used in lower and modestly priced digital/electronic scales, as RF detectors or temperature sensors.

They are quite susceptible to changes in temperature and to electromagnetic interference.

I use a Scott Parker tuned RCBS 10-10 and am very pleased with it.

Handy link to Vishay white paper on Noise Control in Strain Gage Measurements http://www.vishaypg.com/docs/11051/tn501.pdf

Interesting article on Noise Control in Strain Gauge Scales, Steve. I tried looping the power cord through a Ferrite Filter when I was trying to get Strain Gauge Scales to behave. It seemed to help a bit but not enough to make Strain Gauge Scales give me the level of accuracy and repeatability I demand. I finally threw my hands up after 5 different Strain Gauge scales and popped for a Magnetic Force Restoration Scale (A&D FX-120I) and have my Vintage set of Scott Parker Tuned Ohaus 10-10's as backup.

Regards....

 

[SteveOak]

Perhaps you have heard the saying, Swearing is the attempt of a verbal cripple to express himself forcefully.

I came up with an engineering corollary, Ferrites are the attempt of an inept engineer to effect a serviceable design. LOL

Or, there is good news and bad news. We fixed the problem (with ferrites). Unfortunately the plane is now so heavy that we must hire a jockey as the pilot and can only carry 100 pounds of fuel.

Strain gauges are affected by radiated electromagnetic interference as much or more so than by conducted electromagnetic interference so winding the supply cable through ferrites could only address part of the problem and the lesser at that.

Strain gauges are excellently deployed to measure the load factors on steel bridges.

 

[Brians356]

Strain gauges are affected by radiated electromagnetic interference as much or more so than by conducted electromagnetic interference

There is a plethora of radiated electromagnetic radiation, from countless sources, bombarding every square inch of the planet constantly at a multitude of wavelengths. Can you be more specific about what EMR source is likely to clobber a strain gauge? Is it limited to near-field EMR? Does it require EM shielding of the lab to mitigate it?

 

[SteveOak]

Trying not to get too far off topic.

The reasons that the strain gauge type powder scales can have EMI issues are Signal to Noise Ratio and cost. The signal in this case voltage, is very, very small so it would take only a very, very small amount of interference to have a large effect percentage wise.

It is possible to mitigate the effects but the cost of doing so is difficult to justify for a low priced item.

If you have more specific questions, please contact me by PM.

 

[amlevin]

It is possible to mitigate the effects but the cost of doing so is difficult to justify for a low priced item.

And considering that the manufacturer has already done much of this internally with filters it's really unnecessary.

Putting all kinds of power conditioning equipment on the input won't make the scale any more accurate than it's design is capable of.

 

[sparker]

Beam scales: 1.gravity powered (works even when the electricity is out)

2.not susceptible to electric signal interference (see point one)

3. problems are immediately visible

4. can be used with or without a proper zero value (linearity is linearity)

5. perfectly designed for trickling up powder charges.

 

[Brians356]

Beam scales:
...
2.not susceptible to electric signal interference (see point one)

However, beam scales are quite susceptible to static electric charge. (As well might the other types of scales, I don't know.)

I can "levitate" the beam up or down by hovering a fingertip near (but not touching) the pan, if I leave my shoes on while seated at the bench. If I take my shoes off, and place stocking (or bare) feet on the carpet, the static charge does not build up (or dissipates if it is already present.)

Static charge may or may not be immediately apparent.

 

[dixieppc]

Beam scales: 1.gravity powered (works even when the electricity is out)

2.not susceptible to electric signal interference (see point one)

3. problems are immediately visible

4. can be used with or without a proper zero value (linearity is linearity)

5. perfectly designed for trickling up powder charges.

Exactly Scott. Take notice of your Old School Firefighters. Part of each one's PPE/Turnout Gear is an Axe. The new breed will take a chain saw if at all needed. Most present day fire trucks have a "few" Axes on board. The old school boys never leave home without one, usually their own personal one. I'm retired but still have mine. Anyway, the saying goes in Axe vs. Chain Saw circles is: The Axe never runs out of fuel and never refuses to start. That's why I have a set of your tuned Ohaus 10-10's as a trusted backup to my new fangled set of A&D FX-120i digitals.

Regards....

 

[SteveOak]

It is possible to mitigate the effects but the cost of doing so is difficult to justify for a low priced item.

And considering that the manufacturer has already done much of this internally with filters it's really unnecessary.

Putting all kinds of power conditioning equipment on the input won't make the scale any more accurate than it's design is capable of.

It is not necessarily the case that the manufacturer has done all that much. My point is that it is difficult engineering wise and expensive production wise to compensate a strain gauge for the effects of temperature and to mitigate the effects of electromagnetic interference.

An additional concern is that the shielding (using the term in the broad sense since this is not a technical discussions, just an overview) and compensation increase the response time and adversely affect the precision/accuracy/repeatably of the scale. Kind of like wearing mittens. They keep your hands warmer but you can't feel as much.

Around $300 seems to be the price point where compensation and EMI mitigation is done adequately.

 

[sparker]

Discussion of strain gauges ought to be in another thread altogether. The thread title is specific.

 

[Brians356]

sparker,

My comment about static charge relates specifically to beam scales. I would be very much interested in your thoughts and observations on the issue.

 

[sparker]

I load in a room with a vinyl tile floor over concrete. I've never experienced the issue with static charge with a beam scale. I can see how it could happen with carpet and especially if using a plastic powder pan.

Scott Parker