Lightning Strike Protection (SNAP-AILC)


#1

Good Morning,

I am using a SNAP PAC Rack with a load cell module (SNAP-AILC) to monitor the weight on a very large outdoor conveyor scale. The unit we are replacing has a “lightning strike disconnect” puck in between the 4-20mA transmitter and the old input module connected to the controller. This is necessary because the system is a very large metal plant that is outside during storms and has a history of being struck by lightning.

We are eliminating the 4-20mA transmitter and using a 6 lead connection to connect directly to the SNAP-AILC module. What if anything can we use for lightning strike protection between the loadcell and the module (or is this already built into the module itself)?

Best Regards,

Adam


#2

Gudday Adam,

Lightning is brutal. That’s a lot of current (and a just a little bit of voltage :wink: in a really short amount of time.
A strain gauge is working on tiny currents and really small voltages.

If you take a look at the spec sheet for the SNAP-AILC you can see that the module has an over range voltage of around 3.3 to 3.3 millivolts.
So typically its working at less than this when connected to a load cell.
Also note the other two main specs, the ‘Maximum Surivable Input’; +/- 15 volts and ‘Maximum Operating Common Mode Voltage’ of 250volts.
This then I think is your answer to your second question, is lighting protection built into the module?
No.
Air breaks down at around 33 kV per centimeter… so we are well past our 15 volts with just a one centimeter spark.

So, I think the answer to your question is some quality time with Google.
You are looking for a protection device, sacrificial or other wise, that can pass a millivolt signal without attenuation, but block or bypass any voltage over +/- 15v.

Lets know what you find and if it works.
I’m sure many of our fellow forum folks would love to know what you find and your real world experience with said device.

Cheers,

Ben.


#3

You can get load cell summing/trim cards or boards with surge/lightning protection. Check on the internet or go to the big boys like Toledo, Ricelake, GSE…etc


#4

Thanks to all for your input and feedback. I ended up going with an L-COM:

http://www.l-com.com/surge-protector-weatherproof-3-stage-load-cell-rtd-lightning-surge-protector