I have a question on the measurement of ESD shoes. As I go through some of the foot tester there are several brands of foot tester offer to be test in hands free mode where the button is not required to press and the resistance of both shoes in series can be calculated.
What is the working principle behind for this hands free mode and will this test result to be same by using surface resistance meter with handheld probe & 5 pound probe on resistance to ground?
First question, how can a tester be hands free and measure both shoes. If you look at the simple drawing, the tester or meter is measuring the total series resistance of both shoes through the person. For example, if the limit on shoes is 5x107 ohms and each shoe with the person between the right and left show measures 1x107, then the total resistance will be 2x107 ohms and meet the limit set. If the resistance of one show is 1x107 and the other shoe is 3x108 then the total resistance would be 3.1x108 ohms and fail. What you would not know is which shoe failed.
As far as the second part, will this be the same as using a handheld probe and surface resistance meter, if you are standing on a metal plate and the resistance meter is connect in a similar manner, the results may be similar. Usually an integrated tester will only yield a pass or fail while the surface meter may give a results.
Using a 5 lb electrode may yield a different result. Using the electrode instead of a person may not have enough weight and the sweat layer of the person will not be present. To measure a shoe by itself, ANSI/ESD STM 9.1 uses an electrode of 25 lbs to make the measurement.
If you have any other questions, please feel free to add to the forum.
For ESD shoes selection, for example different brands and also we have safety requirement, as the shoes might be used in warehouse, what kinds of tests or parameters should we take into consideration?
For shoes, the qualification requirement test is found in ANSI/ESD STM9.1. This tests a shoe on a metal plate. An electrode is placed in the shoe and then weight is applied to the shoe of 25 lbs. The resistance is then measured and must be less than 1x10*9 ohms.
That is the first part of the test. Then the shoes must be worn and body voltage must be measured on the floor the shoes will be used on.
These tests can be done on any shoes, safety or non-safety shoes.
This standard test method defines a test method for measuring the electrical resistance of shoes used for ESD control in the electronics environment (not to include heel straps and toe grounders).
the tester or meter is measuring the total series resistance of both shoes through the person. For example, if the limit on shoes is 5x107 ohms and each shoe with the person between the right and left show measures 1x107, then the total resistance will be 2x107 ohms and meet the limit set. If the resistance of one show is 1x107 and the other shoe is 3x108 then the total resistance would be 3.1x108 ohms and fail. What you would not know is which shoe failed.