Are the inputs on the Allen-Bradley (A-B) 1769-L1xER high speed?

1769-L1xERLast week a colleague asked me if the inputs on the Allen-Bradley (A-B) 1769-L1xER were high speed inputs, like found on some MicroLogix.

I honestly had no idea, but I was on my way back to my home office so I told him I would look it up and get back to him.

What I found in my research was, when compared to typical the DC input modules like the 1769-IQ16, the 1769-L1's built-in I/O was indeed faster. To illustrate this comparison I have pasted the specs of both below:

1769-IQ16 Input Speed Specs:

1769-IQ16 Input Speed Specs from 1769-IN007

1769-L1xER Embedded Input Speed Specs:

1769 L1 Embedded Input Speed Specs from 1769-TD005

As you can see above, while the 1769-IQ16 has an on / off delay time of 8ms (what I would consider typical,) the 1769-L1 embedded I/O has a much faster 0.5ms on / off delay time – the same as 1734 point I/O modules like the 1734-IB4.

However, this isn't the whole story. While I/O delay time is important, with the CompactLogix and ControlLogix we must also consider if the I/O supports event based tasks, as well as the maximum supported RPI setting.

Dropping the 1769-L1 into RSLogix5000 v20 it quickly became apparent the embedded I/O can not trigger an event based task, as seen in the below screen shot:

1769-L1 Event Task

The final consideration was to find the fastest RPI supported by the L1's embedded I/O. While RSLogix5000 v20 does support a setting of 1ms RPI for the embedded I/O, the below excerpt from the L1 Tech Data sheet reveals that the true limitation is based on the number of modules (including embedded) in a system:

1769-L1 RPI Limits from 1769-TD005

In summary, the 1769-L1 family of CompactLogix processor's embedded I/O contains the same .5ms on / off delay times as many 1734 Point I/O modules of the same type. And while this is considerably faster than standard I/O modules, like the 1769-IQ16 with it's 8ms on / off delay, the speed advantage is quickly lost as you add more I/O modules to the 1769-L1 base system (with a full 8 module system limited to a maximum RPI of 8ms.)

Note: For more details on the 1769-L1 see the Allen-Bradley 1769-TD005 Technical Data Sheet here.

I hope this review of the speed of the embedded DC inputs on the 1769-L1 has been helpful. If you have any comments or questions please don't hesitate to leave them by using the “post a comment or question” link below.

Sincerely,

Shawn Tierney
Automation Instructor and Blogger

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Shawn Tierney

Shawn began sharing automation news and know-how online in 1996 when he launched his first BBS. Then in 1999 he moved to the internet launching ShawnMichael.com, which he later renamed ShawnMTierney.com. In 2013 he moved his automation efforts to a new website, TheAutomationBlog.com, which has since become the most popular independent industrial automation blog on the web.
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