Firejo
Member
Two points;
First, yes, the Rabbit’s aren’t bad, but they are a perfect example of why a common, more expensive solution is better than a cheaper less expensive solution. The Rabbit processors don’t take common code libraries making it very time consuming and thus expensive to integrate them into industrial products. I used to work for a company that used a Rabbit processor for an I/O product and we wanted to make it “Produce/Consume” compatible. We contracted with a company that sold the ability to do that but, in the end, even their solution would have been three to four times as expensive as normal because it was a Rabbit processor. Again, the Rabbit processor works great but code development can be a pain if you want to do something outside of the normal for what they offer.
Seconds, I volunteer for a local fire department and in the past, I was responsible for a support vehicle that had an air system on it. The system got an upgrade that included an PLC controlled air compressor. The company that installed the system went with the lowest bidder who went with an “off brand” PLC that controlled a motor starter that didn’t about 75% of the time when it was cold. So, imagine that we just paid close to, (well I can’t say how much but it was just under seven figures) to have a system overhaul and one of the primary systems wouldn’t start 70% the time when it was below 50° (60% of the time). Turns out that the PLC, that was reading the motor load when trying to start the motor, wasn’t able to get a high enough resolution to make accurate decisions as to the amount of load being placed on the motor when it was trying to start and when it was cold the load was heavier because the oil in the compressor was thicker. There was also a complicating factor in that the low-cost motor starter (rather than a VFD which I would have used) which was providing inaccurate (low resolution actually) load information would give up on its own long before being commanded by the PLC to let go. To further complicate the issue the company that installed the system didn’t really know how to program the PLC because no one there had used that type before so when it didn’t work they didn’t know what to do. They had to call a specialist from the manufacture who wouldn’t help unless he was paid which became a fight between the company that built the system, the company that installed the system and the PLC manufacture that lasted almost three months (in the mean time the air compressor didn’t work).
Fortunately (for the company that did the install), they also miss-wired the 240VAC system on the entire rig and put about 80% of the load on one bank of the AC panel (I’m not an electrician so I might get this next part wrong, it was explained to me about 6 years ago). The compressor would pull from both sides of the 240VAC panel with 80% of the truck’s 120VAC pulling from one side and 20% pulling from the other. Because of the imbalance the motor was showing a very heavy load I believe because the two 120VAC panels were trying to balance out through the 240VAC motor. Again, I’m not an electrician, I sorta get it but I can’t really explain it. The system was “Kinda” repaired in that there are “procedures” in place to start the generator however I’m not responsible for the rig anymore so I’m out of the loop.
Anyway, the point is just trying to figure out why the system didn’t work cost the city about twice as much is it would have cost had they just gone with the proper type of PLC and either a high-end motor starter or VFD. Cheap comes out expensive.
First, yes, the Rabbit’s aren’t bad, but they are a perfect example of why a common, more expensive solution is better than a cheaper less expensive solution. The Rabbit processors don’t take common code libraries making it very time consuming and thus expensive to integrate them into industrial products. I used to work for a company that used a Rabbit processor for an I/O product and we wanted to make it “Produce/Consume” compatible. We contracted with a company that sold the ability to do that but, in the end, even their solution would have been three to four times as expensive as normal because it was a Rabbit processor. Again, the Rabbit processor works great but code development can be a pain if you want to do something outside of the normal for what they offer.
Seconds, I volunteer for a local fire department and in the past, I was responsible for a support vehicle that had an air system on it. The system got an upgrade that included an PLC controlled air compressor. The company that installed the system went with the lowest bidder who went with an “off brand” PLC that controlled a motor starter that didn’t about 75% of the time when it was cold. So, imagine that we just paid close to, (well I can’t say how much but it was just under seven figures) to have a system overhaul and one of the primary systems wouldn’t start 70% the time when it was below 50° (60% of the time). Turns out that the PLC, that was reading the motor load when trying to start the motor, wasn’t able to get a high enough resolution to make accurate decisions as to the amount of load being placed on the motor when it was trying to start and when it was cold the load was heavier because the oil in the compressor was thicker. There was also a complicating factor in that the low-cost motor starter (rather than a VFD which I would have used) which was providing inaccurate (low resolution actually) load information would give up on its own long before being commanded by the PLC to let go. To further complicate the issue the company that installed the system didn’t really know how to program the PLC because no one there had used that type before so when it didn’t work they didn’t know what to do. They had to call a specialist from the manufacture who wouldn’t help unless he was paid which became a fight between the company that built the system, the company that installed the system and the PLC manufacture that lasted almost three months (in the mean time the air compressor didn’t work).
Fortunately (for the company that did the install), they also miss-wired the 240VAC system on the entire rig and put about 80% of the load on one bank of the AC panel (I’m not an electrician so I might get this next part wrong, it was explained to me about 6 years ago). The compressor would pull from both sides of the 240VAC panel with 80% of the truck’s 120VAC pulling from one side and 20% pulling from the other. Because of the imbalance the motor was showing a very heavy load I believe because the two 120VAC panels were trying to balance out through the 240VAC motor. Again, I’m not an electrician, I sorta get it but I can’t really explain it. The system was “Kinda” repaired in that there are “procedures” in place to start the generator however I’m not responsible for the rig anymore so I’m out of the loop.
Anyway, the point is just trying to figure out why the system didn’t work cost the city about twice as much is it would have cost had they just gone with the proper type of PLC and either a high-end motor starter or VFD. Cheap comes out expensive.