wrist strap tester

[tnuflora]

hi...


help me.......


i need a wrist strap tester circuit..
if anybody knows, help me.

 

[KMoffett]

I think that would be an ohmmeter.

What characteristics do you want to test?

Ken

 

[rezer]

I think that would be an ohmmeter.

What characteristics do you want to test?

Ken

Ohmmeters are not a reliable way to test ground straps. I assume he wants a tester to insure he is properly grounded (testing body resistance).

 

[crutschow]

The ground strap tester we use at work is simply a go-nogo resistance checker. You wear the strap, plug it into a terminal on the tester and touch a test terminal with a finger. If the test lamp lights, you're good to go.

Not sure what the resistance limit is but it's probably in the neighborhood of a megohm.

 

[Willbe]

. . .it's probably in the neighborhood of a megohm.

Yeah, designed to bleed off kV's of static charge at a low rate of current flow. Power is Δ(energy)/Δ(time) and the time is lengthened with a high resistance wrist strap so power goes \/.

 

[mneary]

It's a resistance tester that makes sure the resistance is low enough to drain away static. The resistance must also be high enough so it doesn't allow too much current if the user touches something dangerous.

If you 'test' a wire, it should fail.

 

[tnuflora]

hi..

i want to test the wrist strap working or not,before starting my work.


thnx.

 

[3v0]

Edit:
Disregard this post as I was wrong. The following is from a post poster after this one.

Measuring the value of the resistor [470K thru 1M0] and the continuity of the connecting wire will not proof test the strap.

You need to apply a voltage to the strap and the KNOWN ground.

-------------------------------------------------------------------------------
One should be able to test it with a multi meter.

Wikipedia

The wrist strap is connected to ground through a coiled retractable cable and 1 megaohm resistor, which allows high-voltage charges to leak through but prevents a shock hazard when working with low-voltage parts. Where higher voltages are present, extra resistance (0.75 megaohm per 250V) is added in the path to ground to protect the wearer from excessive currents; this typically takes the form of a 4 megohm resistor in the coiled cable (or, more usually, a 2 megohm resistor at each end). Very cheap wrist straps do not have conductive fabric and instead use the fabric to hold the metal plate against the skin, which can result in reduced ESD protection over time as the metal corrodes.

If you have doubts about you DMM in the megaohm range place a 1 megaohm resister between the strap and the ground clip. Then measure the combined resistance. It should read about 500K. I would guess about 25% more or less in either direction would still be OK.

 

[tnuflora]

hi...

i need an alternate methode for checking the wrist strap.
all time i may not be able to measure the resistance using a DMM.
when i am working i w'll be wearing the strap.without removing the strap
from my hand i want to check the strap.

w'll it be possible by using an oscillatory circuit ?

 

[ericgibbs]

hi...

i need an alternate methode for checking the wrist strap.
all time i may not be able to measure the resistance using a DMM.
when i am working i w'll be wearing the strap.without removing the strap
from my hand i want to check the strap.

w'll it be possible by using an oscillatory circuit ?

hi,
Can you say why its necessary to keep checking the grounding strap, its not the usual way.

 

[ericgibbs]

hi...
In my place around 30-35 wrist straps are there..
in working hours every one w'll use one set.
so checking of these many no's using DMM is difficult.
so i need an alternate method...

hi,
Why didnt you tell us that in the first post, we could have saved ourselves some time.

To test a grounding wrist strap requires a KNOWN good earthing point.

Measuring the value of the resistor [470K thru 1M0] and the continuity of the connecting wire will not proof test the strap.

You need to apply a voltage to the strap and the KNOWN ground.

If I gave some instructions on how to construct a test box, do you have the facilities and expertise to make it.?

 

[tnuflora]

wrist strap

hi..

i have all necessary facilities in my lab.


thnx.

 

[ericgibbs]

hi..

i have all necessary facilities in my lab.


thnx.

hi,
This is a very basic tester.

I would use an amplifier across a sampling resistor, that would drive a GO/NOGO buzzer or LED.

Its the Earth loop thats important.

 

[tnuflora]

hi,
Why didnt you tell us that in the first post, we could have saved ourselves some time.

To test a grounding wrist strap requires a KNOWN good earthing point.

Measuring the value of the resistor [470K thru 1M0] and the continuity of the connecting wire will not proof test the strap.

You need to apply a voltage to the strap and the KNOWN ground.

If I gave some instructions on how to construct a test box, do you have the facilities and expertise to make it.?

hi..
i am eagerly waiting for ur replay

thnx

 

[Mickster]

Eric has replied....two posts up from yours.

 

[ericgibbs]

hi tnuflora,
I have designed a more useful circuit using a comparator and LED as a 'PASS' indicator.

If you are interested let me know and will prove the circuit on a project board and post the design tomorrow.

 

[Willbe]

750 K per 250 V = 3 MΩ/kV = ~300 µA through the strap. Undetectible to people and evidently doesn't damage semiconductors, either.

 

[tnuflora]

hi tnuflora,
I have designed a more useful circuit using a comparator and LED as a 'PASS' indicator.

If you are interested let me know and will prove the circuit on a project board and post the design tomorrow.

hi..
i'm really interested in that.
And i have checked the given ckt. that was really nice.but that is not suitable to use in an industry.

thnx

 

[ericgibbs]

hi..
i'm really interested in that.
And i have checked the given ckt. that was really nice.but that is not suitable to use in an industry.

thnx

OK,
Give me 24hrs and I'll post a circuit.

 

[JimB]

hi..
i'm really interested in that.
And i have checked the given ckt. that was really nice.but that is not suitable to use in an industry.

thnx

The why not just BUY ONE!

Spend some money.

JimB