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Joined: Tue Oct 29, 2013 9:08 pm

Replacing old TECO SG2 with RPi

Tue Oct 29, 2013 11:01 pm


I'm on a work assignment to replace some old hardware, a TECO SG2-20HR-D. ... 0HR-D.html

We're using it for a very basic application, sensing 2 pressure switches (GEMS PS75) and actuating one of 2 contactors to power a solenoid A/B valve for forward/reverse in a hydraulic circuit. This is on a large wood grinder, it uses a hydraulic ram to feed material.

Here is the current setup:

Here is what I think could work, by replacing the SG2 with an RPi+3v3/5v conterter+24V relay:

Does this look like it could work? Sorry for the childish graphic but I'm not an electrical engineer and don't have any circuit software.
Also, my boss wants something "plug and play", without any soldering or breakout boards. Ideally something that accepts 5v or 24v hi/lo inputs, can send 24v output, and interface via USB with the RPi. Any suggestions?
This might work? But for $275 instead of about $20. the USB-4761: ... dules.aspx


UPDATE: I found a board from Karlsson Robotics that should work out. ... hannel-io/
4 relays with 5A 110Vac / 24Vdc
6 configurable I/O

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Re: Replacing old TECO SG2 with RPi

Sun Jul 03, 2016 11:44 am

I apologize for dredging up this old post.


Please clean up that wiring. I know you inherited it, but that is pretty horrible. At least add a few terminal blocks and get rid of that 115 volt plug and receptacle.

I have had a few years experience with the SG2 PLC/PLR and the Rpi. For what the Sg2 is and what the Rpi is, I would stick with the SG2 for a few reasons.

1 - it is easily programmable. Ladder programming is quick and easy to learn.

2 - The NVRAM on the SG2 is bulletproof.

3 - It has all that you need in one package including a RTC, DACs, relays, etc.

4 - It is a bit more reliable than the Rpi.

5 - Cost is similar. The SG2 costs about $80-$150 depending on model. The RPI will be at least $80 by the time you are done.

I am not saying that you could not use a RPI to replace the SG2. I am saying that the SG2 is the better choice since it is a machine controller.

If anything goes wrong with the Rpi, it could leave someone liable in the event of an accident. At least the safety auditor will recognize that the SG2 is an attempt to do things "right". A RPI solution would be viewed less favorably to a safety auditor.

The Teco SG2 is sold by a few different people under different brand names. I do not know the real maker is but here is a partial list of makes and models of the same thing

Teco SG2
Siemens LOGO!
Crouzet Millenium3
Allen-Bradley Pico
Eaton/Moeller EASY512
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