mplucker said:
...the + terminal has no wire connected, but the - terminal is connected to a wire labeled 0V (which measures at 4.2mV)...
4.2mV is negligible, but 4.2mV with respect to what? What are you referencing against the "0V" wire to get this reading? Is it connected to the - terminal when you test? Where are you landing your test meter probes?
I would be curious to know where that "0V" wire goes to? If the + terminal is not used then the - terminal is of no real use to any devices and should not really be wired. Unless they were grounding this output supply, which I would not do? But either way, with it not in use there would be no real need to do so?
mplucker said:
...The cable shows USB-1761-CBL-PM02 and I purchased it from
Amazon. It came with a mini-CD with some Chinese drivers, but it installed on my Win7 machine and I was able to access the PLC without trouble.
Yes, you purchased a third party hybrid cable with the USB adapter and 1761-CBL-PM02 all-in-one. This is, of course, not an Allen Bradley manufactured product. I'm glad it worked, but when you specifically mentioned "Chinese drivers", I immediately made a mental comparison between the software world and the automotive world and winced.
mplucker said:
So after I hooked up the computer and went online with the PLC, the I/0-I/3 inputs started working again for some unknown reason. When using the machine, things don't work exactly as they should, but good enough where I can get my stamping work done. The machine is acting as if the switches aren't timed correctly since the pneumatics are not depressurizing at the right moments...
If the "faulty" PSU is disconnected (I would hope it is?), while you await a replacement, then what is currently supplying the input circuits that have allowed them "start working again"? I was under the impression that you cannot use the machine until you replace the PSU? Have you still got it connected up?
That of course is still dependant on whether or not this PSU is actually faulty?
So let's try and determine that...
mplucker said:
...I think my assumption of the Gavazzi PSU being faulty is valid since all the hand and pneumatic switches in question trace back to this PSU. That, and the fact that specs show that it should output 24VDC and it's only at 9VDC between the + and - terminal (with all loads disconnected)...
The specs do indeed say that the PSU is rated 24VDC 30W and also say the trim pot is for fine adjustment between 24VDC and 28VDC and that the DC "out ON" LED comes on at 19.2VDC. This would happen as the DC output voltage climbs at power up. So you cannot adjust this PSU down to anywhere near 9VDC.
The PSU's rated input voltage is 100-240VAC, but can actually be used from 85-264VAC. If the output is measuring 9VDC, with a 118VAC line voltage, then it is most definitely faulty. It also mentions that there is an internal, non user replaceable, T2A fuse on the AC line input side.
mplucker said:
...The switches connected to this PS require 20-30V to function...
This would further strengthen the case that the PSU had to be operating at 24VDC.
So, and with me still not knowing what PSU is currently wired to the inputs (I'm assuming it's still the Gavazzi), then why would the inputs appear to be working, but yet, not quite right, timing-wise?
If you remember back to the good information Ken provided to you with regard to the ON and OFF state voltage levels required for the MicroLogix 1000 inputs - 14VDC ON and 5VDC OFF. The 14VDC is a "soft target" so, and with electronics being electronics, it does not necessarily mean that a lower voltage cannot switch the input to the ON state. If you are currently only switching 9VDC to the inputs, then it would normally not be high enough to switch them to the ON state. However, it is possible that the odd 9VDC signal is doing so, or is doing so intermittently.
This might explain the erratic behaviour of your machine's operations?
If you have some other PSU currently in use, supplying 24VDC for the inputs, then it would appear as though there is some other issue on the machine itself?
Remember, you still do not know what faulted the PSU in the first place? It could just be fatigue, but it could also have been a machine wiring or device fault. Although, nothing seems to be inoperable on the machine when it does work, right?
mplucker said:
...I'm still considering getting a backup MicroLogix 1000 and downloading the program to it so if anything does happen to the PLC, at least I'll have a backup. The electronics on these machines are no longer serviced (except for one company in CA, and I don't want to ship a 3000lb machine).
That would be very prudent.
Regards,
George