2/6/2015 1:34 PM | |
Joined: 9/29/2011 Last visit: 6/6/2024 Posts: 23 Rating: (5) |
Hi, I have a similar problem here with a S7-1212 CPU but AC/DC/RLY. Let me explain. I'm an engineer in automatic and electronic systems. I have fifteen years experience working with PLCs and I work as a teacher in a vocational school here in Spain. I teach PLCs and I've used de S7-1200 as my platform since 2011. I had 20 PLCs S7-1212 AC/DC/RLY reference 212-1BE31-0XB0 with firmware update to V2.3 what it's the latest for this reference. I've used this PLC's with no incidents for three years. The last year I bought 20 PLCs more. In this case the reference is 212-1BD30-OXB0 and firmware 3.0. Now I'm trying to use this new CPUs with my students. The students have to wire some stuff to the PLC like buttons and switchs as input signals, and signaling ligths and contactors. My surprise starts when a student report me some problem about the PLC restarting without reason. First thing I thought was a wiring problem. Is tipical for beginners so I encorauge him to look for the problem. After a few days the problem is still there and is reproducing with more students so, I have to have a look. After a inspection I put away wiring problems. In the diagnostic buffer we can read power down. So I try to isolate the problem. I load a program with a intermittent output to the contactor output. And the problem occurs when the coil is switched off. Then I open a fuse switch for the outputs then the relay is working without load. With this fuse open the problem does not happen. So the problem is the inductive load of the contactor. I monitor the power supply with an osciloscope and I saw inteferences due the inductive load, but in my opinion not to power down the PLC. I know that I have to use suppression circuit for inductive load, but the thing is the contactor is working without load and its a small one( LC1-D09 from schneider with a coil of 230 V AC). And of course if I not install the suppression circuit I can burn the relay output of the PLC but what is happening is another thing, the PLC detect a power down and go to stop. Then restart the system. More than that I use the old CPU and this problem never happens with the same wiring so the thing is that the new PLCs are so vulnerable to interferences or to the quality of the power supply. I dont know if its a question of trying to lower the final prize of the product but in this case its a thing of quality of the final product. In your case that you have a CPU with supply in DC, you can try to put a capacitor of 1000 uF 50 V in parallel with the supply wires in the same conecctor of the CPU and tell us if this solve your problem. In my case I'm still doing probes and I tell us if I find a solution. Thanks in advance
------------------- Splitted from S7 1215 power off randomly. |
Last edited by: Min_Moderator at: 2/6/2015 2:39:31 PMNew subject after splitting |
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