Safeguarding Calibration on Digital Equipment

Cari Spears

Super Moderator
Staff member
Super Moderator
#11
I have never had an auditor ask. I've been doing this for about a dozen years and have worked with 4 different registrars.
 
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Jim Wynne

Staff member
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#12
snglcoin said:
As far as “Real World” issues I can only reference a Quality Digest article written way back in February of 1999. The article doesn’t go into depth about safeguarding equipment but it does point out the ease of which measurement errors can be introduced because of the zeroing capabilities of digital equipment. The link to the article is http://www.insidequality.wego.net/?v2_group=0&p=4499&ct=cdisplay&nt=true&cd_eid=233
The article, while providing useful information, does not reference any actual instances of nonconforming material that resulted from the issue at hand. It serves as a reminder that the potential problem should be addressed, I guess, but it's still theoretical. I've never known of an instance where zeroing a digital device caused problems.

snglcoin said:
It is important to remember the original issue in this thread and that is that ISO requires that measuring devices be safeguarded from adjustments that would invalidate the measurement result. I get the feeling that this is something nobody wants to talk about when it comes to digital equipment. Maybe an auditor will never question our practices but I wouldn't bet on that. I would like to be proactive and I would like gage manufacturers to address the dilemma.
It's maybe a bit much to expect that gage manufacturers would make significant (and costly) design changes if there's no ROI. In order to address your concerns vis a vis the standard, you need to have something in your system that addresses the concern. It's easy enough to demonstrate to an auditor that, A) it's not always possible to directly safeguard the device, and B) you've addressed the potential problem through requirements for recalibration when zeroing has the potential to create problems.
 
G

gaugefixer

#13
Just wanted to add a few things: AAMOROSO - I totally agree with everything you just said.

The zeroing button is there for a reason: use it if you know how to use it. You do not want to hide it or make it inaccessable. If you feel this is a problem with operators then teach them how to use the vernier and how to reset the zero.

If you want to make calipers (digital, dial, scale)tamper proof then here's what you do:
Put a few drops of white out on the adjusting screws of the gib. Loosening these screws to have a smoother feel along the whole length also changes the jaw pressure and how they close.
While white out won't totally stop people from adjustments it will show if someone has made an adjustment.
Adjusting these screws can change your measurements easily by about .005".
 
J

Jeff Frost

#14
JSW05

Gee and all the years I have been using a ASME recognized term Gauge which is an instrument for measuring, testing, or registering pressure above atmospheric pressure and its incorrect English.

You would thank that when an organization like ASME who wrote a pressure gauge, oops gage standard B40.1 would only use those terms recognized in a Quality Dictionary.

Boy that causes my Hysteresis to have a big error, oops can't find Hysteresis in Quality Dictionary. Now what do I.....

Jeff
 

Jim Wynne

Staff member
Admin
#15
Jeff Frost said:
JSW05

Gee and all the years I have been using a ASME recognized term Gauge which is an instrument for measuring, testing, or registering pressure above atmospheric pressure and its incorrect English.

You would thank that when an organization like ASME who wrote a pressure gauge, oops gage standard B40.1 would only use those terms recognized in a Quality Dictionary.

Boy that causes my Hysteresis to have a big error, oops can't find Hysteresis in Quality Dictionary. Now what do I.....

Jeff
If ASME uses the spelling "gauge" to differentiate pressure-measuring devices from other types of measuring instruments and that spelling is understood in the context of some industry jargon, then I'd like to see where ASME makes the distinction. Just because ASME uses that spelling doesn't mean that they intend it to apply exclusively to a certain type of device.

Also, you shouldn't assume that English that's misused in the context of jargon should be considered universally understood. There has been some back-and-forth here regarding differentiating between "objectives" and "goals" when in fact the two are synonymous. Just because ISO 9000 talks about documenting "goals and objectives" doesn't mean that the meanings of the words have changed.
 
A

aamoroso

#16
gaugefixer said:
Just wanted to add a few things: AAMOROSO - I totally agree with everything you just said.

The zeroing button is there for a reason: use it if you know how to use it. You do not want to hide it or make it inaccessable....

That is exactly my point and if your training documentation clearly states that people using measuring instruments should be trained in the proper use of said instruments you are all set.

People can use a micrometer as "C clamp" and ruin calibration, how do you prevent that, TRAINING. In my opinion training someone how to properly use a mic or calipers is "safeguarding against adjustments that can affect the measurement to cause non conforming product."

According to Websters "Safeguard - a: a precautionary measure, stipulation, or device b : a technical contrivance to prevent accident"

Definition A is more applicable where as definition b is what you are referring.

If you removed the ability to adjust you may find it more trouble because then you are removing the ability to make an adjustment that is necessary to achieve a good measurement. You would find a hard time telling a Tool & Die Maker or Mold Maker that they cannot adjust the mics or calipers, there is not a quality expert in the world that would convince them that the rules are such. They would not argue with calibrating, in fact they would tell you I calibrate my tool every time I pick it up, the bi-annual calibration is to satisfy company records, the daily adjustments to the tool is to satisfy their desire for excellance.
 
S

snglcoin

#17
I guess, if an auditor questioned us about this issue, I could reference ISO 10012-1, section 4.12, guidance, where it reads “The requirement for sealing does not apply to adjustment devices that are intended to be set by the user without the need for external references; for example, zero adjusters.” I could also put a written procedure in place stating how we handle digital gages with zero adjustments as an attempt to safeguard adjustments that would invalidate measurement results and train all our users on the procedure. I think that should (or would certainly have to) satisfy any auditor.

I still have a general concern with this issue and although I appreciate the feedback I’ve received on this forum I still think there is a big hole in our ability to safeguard measurement results when it comes to digital equipment. It seems to be a very touchy subject and most people I have talked to about it (and apparently even the standard itself) goes to great lengths to talk around the concern rather than address it directly. It’s these types of issues, however, that tend to come back and bite us down the road. Since digital devices have been around a long time now, our exposure must be limited or we would have had to address it before now. Perhaps it will come proactively in the near future as I have already seen a few digital pressure gages that have password protected calibration settings built into them.
 

Cari Spears

Super Moderator
Staff member
Super Moderator
#18
snglcoin said:
I still have a general concern with this issue and although I appreciate the feedback I’ve received on this forum I still think there is a big hole in our ability to safeguard measurement results when it comes to digital equipment.
Let's get back to JSW05's question about "real world instances"; you referenced a magazine article. What we want to know is YOUR real world instances. What do you make? What digital equipment are you using? What is the skill level of the people using the digital equipment?
 
S

snglcoin

#19
I talked to my Calibration Coordinator about the ISO 10012-1 guidance and he said he would interpret devices with “Zero Adjusters” as “the zero control on an analog meter when changing ranges” which makes perfect sense to me and makes my argument to an auditor very weak.

My real world experiences? I have a digital depth micrometer, which has a resolution of .00005 “and is used to inspect a feature with a .0012”, total tolerance. I had my doubts about the gage at first but I performed a measurement system analysis and found the device to be extremely accurate, repeatable and capable of the measurement in question. It far exceeded any veneer depth micrometer I had ever studied previously. The problem was in setting the zero during calibration. You literally had to “wring” the base to a lab grade surface plate and then bring the spindle gently into contact several times until you got repeatable zero readings. We found any amount of dirt or even oil could cause the readings to be off by as much as .0002” which would be the equivalent of 16% of our total tolerance and cause the system to no longer be valid. We trained all the users to never use the absolute zero setting capabilities of the device and told them if they had any question about the validity of their measurements to being it to the Metrology Lab to be checked. That worked in our situation and even when an operator inadvertently hit the absolute zero button he brought it into the Lab to be reset. However, since the button is exposed it isn’t “safeguarded” and if an operator didn’t recognize they accidentally hit the button all of the resulting measurements would be invalid, including those of the following shifts. It would go completely unnoticed. Did it ever happen? Not to my knowledge but it meant constantly enforcing the procedure with the operators and whenever possible it is better to take that responsibility out of their hands.

Other examples have come from equipment returned for calibration that, when the anvils are cleaned don’t read zero anymore. By as much as .002” in some cases which then caused us to have to investigate the potential for nonconforming material. Which is a nightmare unto itself. Of course I’ve also seen dial calipers returned with the bezel lock unlocked and the bezel free to rotate as you handled the device.

If you were to do an FMEA on a digital Caliper and listed one of the Potential Failure Modes as “invalid zero adjustment” and Potential Effect of Failure as “invalid measurement result” what RPN would you have? I came up with 160, which in our system would warrant a recommended action. About the only thing I could realistically reduce would be occurrence and detection. I can perform training to reduce the occurrence but I would argue that training is not an effective action to address root cause, and it would only have a minimal effect on the resulting RPN. That leaves me with detection, which means design control by removing the potential of an operator inadvertently zeroing the device and invalidating the measurement result.

All I’m asking for is to put the absolute button under the battery cover so it can’t be accidentally hit or provide a menu option with a password protect. Then it is truly “safeguarded.” I still get the feeling like I'm the only one who feels this is an issue. Doesn't anybody else out there see it as an issue?
 

Jim Wynne

Staff member
Admin
#20
snglcoin said:
I talked to my Calibration Coordinator about the ISO 10012-1 guidance and he said he would interpret devices with “Zero Adjusters” as “the zero control on an analog meter when changing ranges” which makes perfect sense to me and makes my argument to an auditor very weak.
Your hypothetical argument. Not to say that there's no value in anticipation, but you shouldn't wear yourself out on the argument before it happens.

snglcoin said:
My real world experiences? I have a digital depth micrometer, which has a resolution of .00005 “and is used to inspect a feature with a .0012”, total tolerance. I had my doubts about the gage at first but I performed a measurement system analysis and found the device to be extremely accurate, repeatable and capable of the measurement in question. It far exceeded any veneer depth micrometer I had ever studied previously. The problem was in setting the zero during calibration. You literally had to “wring” the base to a lab grade surface plate and then bring the spindle gently into contact several times until you got repeatable zero readings. We found any amount of dirt or even oil could cause the readings to be off by as much as .0002” which would be the equivalent of 16% of our total tolerance and cause the system to no longer be valid.
It sounds like a tradeoff question. Do the disadvantages of the digital gage mean that using the analog/vernier type would be more advantageous in the end, all things considered?

snglcoin said:
Other examples have come from equipment returned for calibration that, when the anvils are cleaned don’t read zero anymore. By as much as .002” in some cases which then caused us to have to investigate the potential for nonconforming material.
An error of .002" shouldn't be limited to just digital gages. If there's some junk on the anvils that's .002" across, it's going to be measured regardless.

snglcoin said:
If you were to do an FMEA on a digital Caliper and listed one of the Potential Failure Modes as “invalid zero adjustment” and Potential Effect of Failure as “invalid measurement result” what RPN would you have? I came up with 160, which in our system would warrant a recommended action.
First, it's not a good idea to set "trigger" RPN values. When the "trigger" is say, 150, the highest RPNs you're likely to see will be in the 140's. Also, assignment of RPN factors is almost always subjective. Remember also that they're called recommended actions, not mandatory actions. The expectation is that you'll review the situation for reasonable ways to mitigate risk. It doesn't mean that you must do something that will lower the RPN (hence the risk).

snglcoin said:
About the only thing I could realistically reduce would be occurrence and detection. I can perform training to reduce the occurrence but I would argue that training is not an effective action to address root cause, and it would only have a minimal effect on the resulting RPN. That leaves me with detection, which means design control by removing the potential of an operator inadvertently zeroing the device and invalidating the measurement result.
It seems to me that in your FMEA surmisal that you haven't identified the root cause. Maybe the root cause is "Digital gage used instead of analog." You also seem to be confused about "detection" as it's used in the FMEA context. In this instance it would refer to the relative likelihood of detecting the problem before an "invalid measurement result" occurs.
snglcoin said:
All I’m asking for is to put the absolute button under the battery cover so it can’t be accidentally hit or provide a menu option with a password protect. Then it is truly “safeguarded.” I still get the feeling like I'm the only one who feels this is an issue. Doesn't anybody else out there see it as an issue?
It's a matter of priorities, I suppose. I have a tendency to not worry much about things that I can't control. I think you've identified a valid issue, but short of banishing digital devices from your workplace, there isn't much you can do that you haven't already (admirably) done.
 
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