Would you Calibrate this Digital Hygrometer / Thermometer?

Q

QCALPINE

#1
I have a similar question. I am new to the ISO9000 process. I work for a company that paints parts. We are required to document the temperature and humidity at the time of painting.We use a digital hygrometer/thermometer.Does it need to be calibrated, if so to what standard, if not would a certificate of conformance from the manufacturer be okay? Since this is really just an indicastor of the environment not an instrument that measures the quality of the paint application, I am unclear what as to what level of calibration/cetification is required. Quality manual is vague and I am in the process of rewriting it.
 
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BradM

Staff member
Admin
#2
Re: Would you calibrate this instrument?

Well, hello there! Welcome to the Cove!

If you don't mind, I moved your question to it's own thread and re-titled it. Let me (or another moderator) know if you would like it changed.

Within what range are you needing to fall into, and how accurate is the instrument you are using?

I think you pose a good question. I guess I have been around calibration too long, so I am a bit biased :).
If it is important enough to care about the reading, it's important enough to calibrate.
There is nothing more frustrating than picking up any instrument for whatever purpose, and not having any confidence in it.

You could send it to a competent lab suitable for that instrument, and have it calibrated.
 
Q

QCALPINE

#3
Re: Would you calibrate this instrument?

Brad,
Thanks for moving it to its own thread and the quick reply.
The temperature range we are required to paint under is 60 - 90 degrees Fahrenheit. The humidity range is 20 - 80%.
The instrument came with a certificate of conformance that states range is 14 to 144 degress Fahrenheit and thermometer accuracy is +/ 1 .8 degrees Fahrenheit.
The range on the hygrometer is 5 - 95 % relative humidity and the accuracy is +/- 5 %.
 
J

jem63

#4
Re: Would you calibrate this instrument?

I have a similar question. I am new to the ISO9000 process. I work for a company that paints parts. We are required to document the temperature and humidity at the time of painting.We use a digital hygrometer/thermometer.Does it need to be calibrated, if so to what standard, if not would a certificate of conformance from the manufacturer be okay? Since this is really just an indicastor of the environment not an instrument that measures the quality of the paint application, I am unclear what as to what level of calibration/cetification is required. Quality manual is vague and I am in the process of rewriting it.
I think the magical sentence in your question is.

"We are required to document the temperature and humidity at the time of painting."

If you are required to test your process the instrument you use should be calibrated.

The certificate from the manufacturer should suffice. I would also contact the manufacturer to identify what NIST or similar standard is used.
 
H

Howard Lee

#5
Re: Would you calibrate this instrument?

Brad is right, "If it is important enough to care about the reading, it's important enough to calibrate." As I understand it, the evironmental conditions (temperature/humidity) are often an indicator of the final quality in a painting process. If you document the temperature/humidity, would you really want to use a guage that you aren't sure of.
 
Q

QCALPINE

#6
Re: Would you calibrate this instrument?

The certificate of conformace states that the thermocouple base and noble metals conform to ISA Limits of Error Standard MC96.1. I am going to give them a quick call and see what this means and how it relates to the accuracy of the temperature and relative humidity. Both ranges are signifanctly greater than what I need to read, not that it probably makes any difference.
 
K

Kevin H

#7
Re: Would you calibrate this instrument?

I've got to agree that you should be calibrating your instruments, as you're using them to document compliance to process requirements. The certificates of conformance from the manufacturer are adequate for the instruments as received. That doesn't mean they're adequate 1 or more years from initial receipt.

You need to assure that they are accurate on an ongoing basis. That implies determining some sort of time interval over which you use them, and then calibrate them either internally or externally. A calibration report should include as-found condition, as-left condition, accuracy, traceability to NIST standards, etc.

Your saving grace, is that you have fairly wide ranges for your process variables versus the accuracy of the instruments being used.
 
J

JHagani

#8
Re: Would you calibrate this instrument?

IMHO, the Cert of conformance is not the same as calibration records.

A COC says your machine should work correctly, if nothing elese has gone wrong.
A calibration verifies your instrument is actually performing correctly within the given range.

That is the reason, you should verify every new inspection equipment before first use.

When I bought my humidity/temp gage, the seller offered to have it calibrated for an extra cost, think it was $35. But my procedures require me to have my calibration house accrediated to ISO 17025.
 

Jim Wynne

Staff member
Admin
#9
Re: Would you calibrate this instrument?

The certificate of conformace states that the thermocouple base and noble metals conform to ISA Limits of Error Standard MC96.1. I am going to give them a quick call and see what this means and how it relates to the accuracy of the temperature and relative humidity. Both ranges are signifanctly greater than what I need to read, not that it probably makes any difference.
It does make a difference. Some factors to consider:
  • The process tolerance. How much variation can your process stand in terms of temperature, humidity, and the interaction of the two? What sort of bad things might happen if the limits are violated?
  • What is the likelihood that the limits will be violated? You need to understand the variables involved before you can determine the extent of control you need to invoke. Controlling things that don't need to be controlled--or controlling them to a greater extent than what's actually necessary--is just as wasteful as letting something bad happen before you do anything.
The bottom line is that if you understand the process and the variables that contribute to nonconformance, you don't need to ask whether or not a given device needs to be calibrated. The question will answer itself when you understand the process.
 
J

jfgunn

#10
Re: Would you calibrate this instrument?

My simple answer to your question is YES. Have it calibrated. The long answer follows:

Have you ever had to stop painiting parts because the temperature or humidity was out of the range? If yes, then it is good that you are recording it. If not, what is the point of recording it?

If the temp or humidity is out of spec, what does it do to the product and would this be caught by some other quality inspection. (ie, the paint goes on poorly and you do a visual check at the end for surface finish or you do some other test to the part). If this is the case, then you may not need to record it.

Let's assume that you have to record it and none of the questions above gave reason to stop recording it (or the president of the comapny wants you to record it and he is the boss so you are going to do it.)

My question would be : Do you need to calibrate the one you have to make sure that it has been good for all of the years that you have used it? OR do you want to get it calibrated for the furture? What will you do if it is found to be bad? Most likely, you will just do nothing and buy a new one.

All of that being said, ISO 17025 accredited calibration of a temperature/humidity meter is about $85. A new meter can be purchased from Fisher Scientific with an accredited certificate that has a two year due date for about $50-$60. Go to www.fishersci.com and search for "traceable temperature humidity". With the tolerances you have, you could buy a new gage fro fisher and do a single point comparison between the new gage and the old gage to confirm that the old gage was actually working for the past few years. Note also, that if you send the gage out, someone will ask, "how did you record temperature and humidity when the gage was out for service?"

Knowing that you can buy a new one with a cert for less than the cost of calibrating the old one, please do not make the mistake of just buying a new one with a cert every year or two. Remember, there are two points to having something calibrated: 1.) to have confidene that it is making a good measurment now 2.) to know that is has probably made good measurements since the last time it was calibrated.


Joe
 
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