Replacing 1771-ASB with 1785-LT Issues

[Microbictomb]

So I have 3 racks with a 1785-L40/B processor. Channel 2A runs rack 3 with a 1771-ASB remote adapter in scanner mode. I received a 1785-LT as a spare and I wanted to test it out as a remote adapter and/or scanner module.

I have the switch settings correct according to the manuals. I am not getting a response from the LT in the channel status. The channel configuration set for scanner mode seemed to be the first/easiest option to test it out but I get no response and switching to adapter mode gives the same results.

Channel 2A status LED flickers green really fast while in scanner mode and is solid green in adapter mode on the L40, the REM I/O LED on the LT is solid red in scanner mode and green/red flashing in adapter mode.

This is a simple ladder for testing I/O but if anyone has a suggestion for this new connection I would greatly appreciate it.

Thanks,
Jon

 

[danny.michael]

The 1785-LT is a PLC5 processor. It cannot be used to replace a 1771-ASB remote I/O adapter. Setting a PLC5 channel to adapter mode is a whole different animal than a remote I/O adapter.

 

[Microbictomb]

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1785-um001_-en-p.pdf

Page 19 of the manual. It just doesn't get much more descriptive after that page. And the LT has a scanner mode switch setting. Any idea why if you cannot use it in that mode?

"Use a Classic PLC-5 processor (except the PLC-5/10 processor) in adapter
mode when you need predictable, real-time exchange of data between a
distributed control PLC-5 processor and a supervisory processor. You
connect the processors via the remote I/O link (see Figure 1.3). You can
monitor status between the supervisory processor and the adapter-mode
PLC-5 processor at a consistent rate (i.e., the transmission rate of the
remote I/O link is unaffected by programming terminals and other
non-control-related communications). "

 

[danny.michael]

The 1771-ASB is used to control I/O modules in a chassis, acting as a remote I/O adapter to a PLC5 channel that is in scanner mode.

The 1785-LT is a PLC processor that, in scanner mode, can control I/O in a remote chassis. If the -LT is placed in adapter mode it will appear to another PLC5 as a remote I/O rack. But it does not act as a remote I/O adapter in the sense that the scanning processor cannot directly control I/O modules in the same chassis with the adapter mode PLC.

Setting a PLC5 processor to adapter mode is used, just as the manual says, when you need predictable, real-time exchange of data between a
distributed control PLC-5 processor (the processor in adapter mode) and a supervisory processor (the PLC in scanner mode).

It's been a long time since I've set up a PLC in adapter mode and I don't remember all of the details. If your intention is to use the -LT in place of a -ASB, then you're going to find that it doesn't work. If you want to experiment with data transfer between two processors over a remote I/O link then you have more to do in understanding the manual and its explanation of the adapter mode processor application.

 

[Microbictomb]

That makes much more sense to me. Thank you sir, I appreciate the help

 

[vikas1947]

1771-ASB replacement option

is there any other module which i can use in the place of 1771-ASB because it is discontinued

 

[Ken Roach]

The 1771-ASB had a good run, but it's the only device that does what it does.

You can buy them new until the end of 2015.

While you could conceivably use a PLC-5 controller as an adapter and then have it control the I/O in turn, it wouldn't work the same and would be much more expensive, and would suffer similar availability problems.

 

[vikas1947]

product got discontinued

as i searched the life cycle of product it is discontinued so from where i can buy new one .

 

[sthompson]

That is the Remote I/O Adapter for the SLC500 PLC Line (1747) no the PLC5 Line (1771).

Stu....

 

[vikas1947]

yes i need a replacement for the remote i/o adapter as it got discontinued

 

[Doug-P]

http://products.plccenter.com/

They might have some.