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To Calibrate or Not to Calibrate various Weight Scales

M

michaelkhart

#1
I have a client that has weigh scales in both their receiving department and mixing department. They use the scales for overall verification of weights when materials come in and when materials are mixed together in a vat. Although they verify that the weight measurements they are getting from the scales are in the ballpark by checking with objects of known weight, they are not concerned with the level of precision for either application. The mixed materials undergo specific visual inspections later on in the process and they have never had an issue where the mixed product had to be rejected. They have assessed the risks of mixing with a weigh scale used for reference only and have decided that the cost of verification/calibration is much more than the cost due to risk of product batch failure. Therefore, since product inspection related to proper mix of materials is carried out later on in the process, they have decided to remove the weigh stations from a calibration program and label them "not calibrated - use for reference only".

Personally, I agree with their reasoning, and their right to make this decision. As long as their product quality is protected through the product inspection later in the process, the organization should be able to weigh the risks/costs of calibration. Thier ISO 9001 Registrar may not agree.

What are your views?
 
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M

michaelkhart

#3
Re: To Calibrate or Not to Calibrate

It means that they have assessed the potential probability and costs of having to reject and scrap a batch of mixed materials because they did not have the mixing room weigh scale on a formal verification/calibration program.
 
D

Duke Okes

#4
Re: To Calibrate or Not to Calibrate

It's not the registrar's decision. It is a business decision made by the company, with rationale they can support with data.
 

somashekar

Staff member
Super Moderator
#5
Re: To Calibrate or Not to Calibrate

I have a client that has weigh scales in both their receiving department and mixing department. They use the scales for overall verification of weights when materials come in and when materials are mixed together in a vat. Although they verify that the weight measurements they are getting from the scales are in the ballpark by checking with objects of known weight, they are not concerned with the level of precision for either application. The mixed materials undergo specific visual inspections later on in the process and they have never had an issue where the mixed product had to be rejected. They have assessed the risks of mixing with a weigh scale used for reference only and have decided that the cost of verification/calibration is much more than the cost due to risk of product batch failure. Therefore, since product inspection related to proper mix of materials is carried out later on in the process, they have decided to remove the weigh stations from a calibration program and label them "not calibrated - use for reference only".

Personally, I agree with their reasoning, and their right to make this decision. As long as their product quality is protected through the product inspection later in the process, the organization should be able to weigh the risks/costs of calibration. Thier ISO 9001 Registrar may not agree.

What are your views?
Hello Michael.
There are two aspects here.
1. Statutory:
I do not know where you come from, but over here in India, all industrial and commercial weigh scales are coverd under the department of weights and measures and they are duly stamped. These have to be renewed every year by approved evaluators of the department which is a government body. Every weighscale purchased is delivered with the stamping on the label and a certificate. Please check if something similar applies in your region.
2. Requirement:
What ever be the ballpark tolerance that is acceptable, still this measure does fall under the monitoring and measurement that is undertaken and hence this monitoring and
measuring equipment (weigh scales) needs evidence of conformity of product to determined requirements. Hence calibration, and the above will meet this if such a statutory operates in your region.
 
S

samsung

#6
Re: To Calibrate or Not to Calibrate

since product inspection related to proper mix of materials is carried out later on in the process, they have decided to remove the weigh stations from a calibration program and label them "not calibrated - use for reference only".
They can skip calibration of the weighing scales at this stage if these devices aren't used for determining the acceptability of products or process parameters. However, it's also implied from your above statement that they are using calibrated equipment later on in the process in order to qualify the product quality.
 
M

michaelkhart

#7
The inspection later on in the process is visual and include appropriate instructions and colour templates that look for applicable characteristics of the mixture.
 

Stijloor

Staff member
Super Moderator
#8
Re: To Calibrate or Not to Calibrate

It means that they have assessed the potential probability and costs of having to reject and scrap a batch of mixed materials because they did not have the mixing room weigh scale on a formal verification/calibration program.
Let's assume that due to some inadvertent mishap, the scale is off by some weight value, you would have no way of knowing..and how would that affect the process/product?

Stijloor.
 
S

samsung

#9
Re: To Calibrate or Not to Calibrate

Let's assume that due to some inadvertent mishap, the scale is off by some weight value, you would have no way of knowing..and how would that affect the process/product?

Stijloor.
As the OP submitted in the first post that they are verifying the scales against some known weights.

Although they verify that the weight measurements they are getting from the scales are in the ballpark by checking with objects of known weight, they are not concerned with the level of precision for either application.
 
S

samsung

#10
The inspection later on in the process is visual and include appropriate instructions and colour templates that look for applicable characteristics of the mixture.
Since the requirement of calibration falls under section 7, it's permissible to exclude calibration from the scope specifying valid justification.
 
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