Should a low cost hand held refractometer be in a calibration program?

Jim Wynne

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#2
Should a low cost hand held refractometer be in a calibration program or simply zeroed at each use?
There's a third possibility; it should be in the calibration system and be zeroed prior to use. :D
You haven't provided enough information. What's it used for? Is this an ISO 9001 (or some other standard) system? What's the risk if the thing isn't periodically calibrated?
 

yodon

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#3
Jim, as usual, makes good points.

I'll just add that cost is irrelevant to a calibration program. Either the equipment should be calibrated or not. If (presuming Jim's criteria) quality decisions are made, then it likely should be. If it makes ense to purchase a new one rather than re-calibrate an out-of-calibration one, then consider that option.
 

Ron Rompen

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#4
I agree with Yodon. Cost cannot be used as a factor when considering whether or not to perform calibration (although it may be considered, along with the potential for error and the results of that error) when determining the frequency of calibration.

Zeroing out any measuring instrument prior to use has no impact on whether or not the instrument measures accurately; that is the purpose of the calibration procedure.

If it sufficiently inexpensive, put it on a 1 yr (or whatever period is appropriate) replacement schedule, and be prepared to explain your rationale for this to your auditor.
 

adickerson

Inactive Registered Visitor
#5
If it is cheep it may have never have been calibrated, even by the factory. Just becasue it is new does not mean it is even close to accurate. I would test the device against known samples before I ever used it. You may not need to strictly "calibrate" it but a verification is defiantly in order.

Remember, things that are seen as cheep and disposable get the most abuse. I saw some on pry the top of a oil can with a digital caliper - that is precision machining!
 

AdamP

Inactive Registered Visitor
#6
To answer your question, you might consider how the refractometer is used. What decisions are made from the readings produced, and critical is the data? As already noted, even brand new, a unit could produce incorrect readings, so zeroing and calibration would make sense, but since it's just a tool, you really need to understand how and why you are using it and what you are doing with the results. That will tell you all you need.

Cheers,

Adam
 

bobdoering

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#7
Typically, the gage is used to determine concentrations, such as concentration of coolant in a machining center or soap in a washer. So, you can calibrate it by preparing standard concentration solutions and ensuring it reads the value correctly. If not, it will allow you to make incorrect decisions. Gage calibration minimalists will say that if it has no direct impact on final dimensions there is no need. If you have to rework a few skids of parts because the soap concentration on a wash was too little - or too much - then you get to learn the lesson the hard way. You might not notice on the coolant - until somebody realizes how much money they were wasting on prematurely worn tooling.
 

mecramur

Inactive Registered Visitor
#8
All, thank you for all the great information. I have been busy and just now checked the thread.

The refractometer is an inexpensive $130 hand held unit. It was purchased to check the concentratkion of water in oil used in a grinder. There is suppose to be 1 part DI water to 25 parts of oil. They are currently and have for some time been just mixng the fluid and not checking concetrations.

The instrument did not come with an RI for their specific chemistry but the tech did find a crosss reference chart for oil. The cross refernce syat the conctration of water is really 2% not 3.8%.

I questioned the cross reference accuracy and asked them to create a control sample, mixing 1cc of di water to 25 cc of cutting oil and then make several measurements with the new refractometer. This to me was a validation of the instrument and the readings and of the cross reference. This sample mixture could then be used to validate the instrument before each use.

What is the repeatability and accuracy of these hand held units?

Can these actually be calibrated or just verified?
 

Jim Wynne

Forum Moderator
Moderator
#9
All, thank you for all the great information. I have been busy and just now checked the thread.

The refractometer is an inexpensive $130 hand held unit. It was purchased to check the concentratkion of water in oil used in a grinder. There is suppose to be 1 part DI water to 25 parts of oil. They are currently and have for some time been just mixng the fluid and not checking concetrations.

The instrument did not come with an RI for their specific chemistry but the tech did find a crosss reference chart for oil. The cross refernce syat the conctration of water is really 2% not 3.8%.

I questioned the cross reference accuracy and asked them to create a control sample, mixing 1cc of di water to 25 cc of cutting oil and then make several measurements with the new refractometer. This to me was a validation of the instrument and the readings and of the cross reference. This sample mixture could then be used to validate the instrument before each use.

What is the repeatability and accuracy of these hand held units?

Can these actually be calibrated or just verified?
Checking the device against a control (a standard) is calibration. You can test the device for repeatability, reproducibility, etc. by performing the appropriate measurement system analysis.
 

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