Lower limit should be 8 x 10E5 ohms (800 kilohms) so most Testers would be
set at 750 kilohms.

 

I think the only way to fail low is some parallel ground path.

 

Here's some information form the foot grounder standard practice ESD
SP9.2-2003 Footwear - Foot Grounders Resistive Characterization (not to
include static control shoes):

 

APPENDIX C -Parallel Ground Paths

A parallel ground path allows a flow of electrical current through a path
that is not intended for the test. Parallel ground paths may be caused by
several different situations.

 

For example:

a. The path represented by the person standing with one shoe on the floor
and the other shoe on the test apparatus. A parallel path may be created by
the shoe on the floor. Current from the test instrument is then directed
down two paths when it was intended to be directed down one. The correct
path for the test is with one shoe in the air or on an insulating surface
and the other shoe on the test plate.

b. The path presented by a person inadvertently supporting themselves by
means of one hand on another object such as a wall, table or supporting
member in order to measure the resistance in one foot contact. The hand has
created a parallel path to ground.

c. The path represented by a person leaning against another object with
other parts of the body in order to provide physical support during a
testing sequence. This can then lead to other grounding paths and erroneous
results.

 

APPENDIX E -Foot Grounder Classification


Electrical

Resistance Value*


Foot Grounder Standard Use Type A

8.0 X 10^5 to 3.5 X 10^7 ohms


Foot Grounder Special Use High Type B

3.5 X 10^7 to 1.0 X 10^9


Foot Grounder Special Use Low Type C

<8.0 X10^5

 

 

Gene Felder

[log in to unmask]

 

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: Wednesday, May 20, 2009 2:40 PM
To: [log in to unmask]
Subject: Re: [TN] ESD Heel Strap / Shoe Checker - low resistance

 

Which low limit does he fail? Our operators work to the recommended  

limits but your Esd controller can permit higher and lower limits if  

they consider that ok. We allow visitors who are not allowed to touch  

product to pass on a tester set to the wide limits.

Rex

 

Sent from my iPhone

 

On 20 May 2009, at 19:58, "Helena Pasquito (Cobham DES SSA)"
<[log in to unmask] 

 > wrote:

 

> Hello Tech Net,

> Assemblers and techs check their shoes on an ESD Shoe checker, each  

> day before the start of their shift. We have one person that works  

> in the warehouse that always fails low (resistance). We have tried  

> new heel straps, walking for an hour or two in regular ESD shoes,  

> even wearing someone elses shoes that had just passed. Nothing seems  

> to work. He has also tried to apply lotion to the strap that sits  

> inside his sock. Do you know of any tricks we can try to employ?  

> Have you seen issues like this before? I think some of the steps we  

> took may have helped for a high resist fail but not a low resist.  

> Even the wrist strap test fails for him (multiple wrist straps).   

> Any suggestions would be much appreciated.

> Helena Pasquito

> Training Specialist

> Certified IPC Trainer

> Cobham Electronic Systems

> 1001 Pawtucket Blvd., M/S 160

> Lowell, MA 01853

> 978-442-5024

> [log in to unmask]

> 

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