Resin encapsulation?

[BC SYSTEMS]

Sorry,

Giving you a bashing this week!

I'm working on a project in the Sahara and they have alot of issues with dust and sand and vibration proofing their equipment.

Have you or any of your customers resin encapsulated a PLC board?  I was thinking of going upto the base of the IC holders so any IC's could be replaced, anything else would be PLC write-off?

Do you think heat dissipation would a problem?  Other than the main CPU and maybe the PSU regulators are there any other parts that generate excessive heat?

Many Thanks

[support]

Since the PLC uses socketed components it is not suitable to be coated in resin. Liquid state resin could flow into the socket and potentially create an insulation between the pin and the contact. And yes, heat dissipation is another potential problem.

A better solution is to use a environmentally sealed box that can withstand the type of environment that it is designed to protect.

Regarding your question about mapping DM to single bits we have a response at the feedback/opinion forum. Thank you for your input.

[BC SYSTEMS]

Hi,

Thanks for the response.  I was only thinking of going up to the base of the IC i.e. the soldered part so would only be 1-2mm at a guess?

What is the heat dissipation of the PLC (F series for example), some of the environments I work in are very unforgiving and I would worry about the final temp of the PLC in a sealed type box.

Cheers

[support]

If the coating is only up to the solder part of the IC pin then that should be OK.

The F-series PLC can operate between 0 and 70 degree C. Excluding load current an F-series PLC consumes < 120mA @24VDC which means it dissipate < 3W (i.e. less than a 4W night light bulb). Ideally your sealed enclosure should have filtered force air ventilation. Otherwise use a more airy enclosure to allow natural convection to dissipate heat from the CPU area.

[ccdubs]

Reviving an old post here but I am having an issue with a couple of installations where we see our analogue inputs randomly and intermittently dropping to 0 on FM88 PLC's. These seem to occur when there is a chance of high humidity and potentially condensation in the cabinet, which we obviously try to avoid. To try and prevent this from happening I was looking at using a lacquer spray like the one linked below to coat both sides of the PLC.

Can you confirm whether this is OK to use and whether there are any components we should cover before spraying? I'm not too worried about issues around being able to replace components as we haven't had to do that for a very long time.

http://www.jaycar.co.nz/Service-Aids/Chemical-Aids/Aerosols/Circuit-Board-Lacquer-Spray-Can/p/NA1002
 

[support]

Does humidity cause the ADC to drop to 0? How long did it stay at 0? If it is condensed water the bad reading should persist for a while. But if it flashes and go off it could be noise pulse?  You could try some software filtering

The lacquer coating may be ok to apply the SMD IC pin but avoid the socketed component as mentioned in the original post.

[ccdubs]

The PLC's are polled at 10 minute intervals so it is hard to know how intermittent the fault is. I haven't seen the values at 0 for longer than one poll. When the error happens all inputs fall to 0.

[support]

Are you polling the PLC's data from a computer? Do check that the communication is successful by verifying the header and the checksum field?

This is to prevent using data from a failed communication which may not reflect the actual state of the data inside the PLC.  If you are only polling once every 10 minutes you may may a few times and check the data for consistency.

[ccdubs]

I am using MODBUS RTU with error checking. In the case of a communications error the SCADA values are not overwritten so I am confident that the analogue drop outs are not coms related.

[ccdubs]

Revisiting an old thread again...but this has recently become an issue for me and I realize that I never got an answer to the question regarding application of a lacquer.

[support]

You can apply lacquer to all the SMD components. For the main CPU only apply lacquer to the CPU pin but not the body because we want to avoid increasing the thermal resistance of the CPU body due to the laquer.

For socketed component, you can apply laquer to the bottom of the socket but do not spary over the IC socket since the coating may cause contact problem between the IC pin and the socket.

[ccdubs]

Thanks for the answer.