Is there a standard for testing equipment at a single point?

[CLaurenceH]

Is there a standard that states that a single test point is acceptable for certain circumstances?

We have an auditor having concerns that we check some equipment to just a single test point. Such as Timers, some environmental monitoring systems and some ovens that are used at a single point.

If we don't find some kind of industry standard then we are going to have to set up some kind of range for all these items.

Just thought I would check in here.

Thanks

 

[AndyN]

Re: Oven Calibration Range: How many points?

Is there a standard that states that a single test point is acceptable for certain circumstances?

We have an auditor having concerns that we check some equipment to just a single test point. Such as Timers, some environmental monitoring systems and some ovens that are used at a single point.

If we don't find some kind of industry standard then we are going to have to set up some kind of range for all these items.

Just thought I would check in here.

Thanks

What's the spec? I'm guessing there's some kind of range... Did your auditor say anything other than a single point isn't much use? They are correct, but that's not really much help as a statement from them, is it?

 

[BradM]

Re: Oven Calibration Range: How many points?

Is there a standard that states that a single test point is acceptable for certain circumstances?

We have an auditor having concerns that we check some equipment to just a single test point. Such as Timers, some environmental monitoring systems and some ovens that are used at a single point.

If we don't find some kind of industry standard then we are going to have to set up some kind of range for all these items.

Just thought I would check in here.

Thanks

I do not know of a specification.

What is your range of use? If you have, say, an oven that is only used at 50?C and isn't ever changed from that test point, then a single point check is OK.

However, as a general rule, equipment needs to be verified across the use range.

Timers are a bit more involved, as you test the timers at a certain interval/accuracy stated (?5 sec/day).

If you can provide a little more information regarding your calibration test points, relative to how you use the equipment, that would help.

 

[BradM]

Is there a standard that states that a single test point is acceptable for certain circumstances?

We have an auditor having concerns that we check some equipment to just a single test point. Such as Timers, some environmental monitoring systems and some ovens that are used at a single point.

If we don't find some kind of industry standard then we are going to have to set up some kind of range for all these items.

Just thought I would check in here.

Thanks

I moved the posts to where you can have your own thread to discuss the subject.

 

[AndyN]

Typically, 3 types of study would be performed to tell you more about the calibration needs: "Linearity", "bias" and "stability". It may not be all three studies are needed, but most would see that, for example, an over might take a while to get hot and stay there during the working shift (stability), the equipment may not read - as Brad is suggesting about the range/spec - in a linear manner. It might be that, depending on certain factors, bias may come into play, too. It's best to run a study, so you can show if a single point is all that's needed.

 

[dgriffith]

An oven temperature controller should be checked electrically by resistance substitution (for RTD input) or voltage (for T/C) over it's range. The controlling probe used to sense temperature inside the oven should be checked using a meter to read resistance (RTD) or voltage (T/C) and some type of temperature bath/dry well.
Using a standard probe located near the sense probe, the oven can be checked for 1) systematic bias at the temperature of interest (how much to offset the setpoint by to get the temperature you really want), and 2) how well the oven can control that temperature (stability).

For a timer, NIST Special Publication 960-12 Stopwatch and Timer Calibrations, a recommended practice guide, might prove noteworthy.

For environmental, since temperature changes/swings are the norm, I would have those calibrated as any other MTE--across the specified range(s)

 

[BradM]

An oven temperature controller should be checked electrically by resistance substitution (for RTD input) or voltage (for T/C) over it's range. The controlling probe used to sense temperature inside the oven should be checked using a meter to read resistance (RTD) or voltage (T/C) and some type of temperature bath/dry well.
Using a standard probe located near the sense probe, the oven can be checked for 1) systematic bias at the temperature of interest (how much to offset the setpoint by to get the temperature you really want), and 2) how well the oven can control that temperature (stability).

For a timer, NIST Special Publication 960-12 Stopwatch and Timer Calibrations, a recommended practice guide, might prove noteworthy.

For environmental, since temperature changes/swings are the norm, I would have those calibrated as any other MTE--across the specified range(s)

Agreed all the way around.

A note about ovens...

So much depends on the initial qualification/intent of what the oven is going to do perform.
In addition to the good information above about an oven calibration, you also have to consider the uniformity inside, and how it relates to the temperature controller.

Personally (just Brad) I don't really like single point calibrations, as I don't think any one device is just used at one point. However, there are sometimes long-term stability studies in an oven at one temperature. When justified, I think it's OK to place a probe in the working zone and check the controller.

The best method is to perform uniformity studies and relate to the recording device on the oven; with the recording device calibrated. The acceptance of the oven run is then confirmed by the recording data.

Then the temprature controller almost becomes a reference only device.

I would also be interested to know if these instruments were qualified for single point use, and tagged/labeled as limited calibration; single use point calibration. If not (IMHO) the use of single point calibration is definitely something to look into.

 

[AndyN]

As a heat treatment process, the BEST way to check the performance is to use this: http://www.astm.org/Standards/A991.htm

It may be your auditor knows less than you imagine...

 

[BradM]

As a heat treatment process, the BEST way to check the performance is to use this: http://www.astm.org/Standards/A991.htm

It may be your auditor knows less than you imagine...

I've never seen that one. Thanks Andy.

I know for aerospace, AMS2750 is a good one.

 

[dgriffith]

Then the temprature controller almost becomes a reference only device.

With our small environmental chambers (2-5 cu. ft.) we use a working standard probe and thermometer readout for recording actual temp. The air inside is stirred to reduce gradients/increase uniformity, and the job of the temp controller is only to be a stable controller; we adjust the setpoint as required to achive the desired temp.