To go through the specs for the 1769-L30ERMS:
16 Ethernet Nodes means you can have 16 ethernet devices defined in your "tree". These can be VFD's, encoders, barcode scanners, or I/O racks. An I/O rack is just
one node, regardless of whether it has 1 card on it or 50. The number of cards will affect the number or
connections, but that's not the same as the number of nodes and is, for practical purposes in the case of your PLC selection, irrelevant.
I/O Capability Expansion of 8 means that you can add 8 1769 cards to the local rack (i.e. tacked onto the RHS of your processor). The usual restrictions regarding power supply distances etc apply.
When it comes to safety I/O, yes, you'll need to use a remote chassis for your safety I/O. There is no 1769 series safety I/O on the market. 1734 Point I/O is a common choice. So you'll add a 1734-AENT(R) to your ethernet tree; that will take up one of your 16 nodes (or 48 nodes, if you're using an L36). You can then put as many safety I/O modules on there as you like - it's still only one node.
The limitations you will face are in the arrangement of your 1734 chassis. There are two factors to consider; bus power and the number of CIP connections your AENT(R) can make to its I/O modules (note that this is completely separate from, and unrelated to, the number of connections you
PLC can make. This is about how many cards your 1734-AENT(R) can talk to on it's local bus, not how many I/O racks your 1769-L30ERMS can talk to over ethernet).
First; bus power. Your 1734-AENT(R) can supply a certain amount of bus power. Each card on your rack draws an amount of bus power. Obviously, if the second number is bigger than the first number, you're going to have issues. The solution is pretty simple; once you have added so many cards that your AENT(R) is at its bus power limit, add a 1734-ED24DC to the chassis. This is a "bus power extension module" and does exactly what the name suggests - provides all the modules to its right with bus power once the AENT(R) has exhausted its resources. There's an
RA technote (techconnect required) that will help you calculate your bus power requirements - note that the 1734-AENT, 1734-AENTR and 1734-EP24DC all have different amounts of available bus power. Alternatively, RA's free IAB software will let you create a mock-up of your rack and it will warn you if you exceed the allowable bus power and offer suggestions on how to reconfigure things.
The CIP connection limitation is a bit less, uh, straightforward. The newest 1734-AENT(R) modules support 5 rack optimized connections or 31 direct CIP connections
if only standard modules are used. As soon as you put a safety card in the rack, that drops to 20 CIP connections. A 1734-OB8S uses two CIP connections - one for input data and one for output data. You need both input and output data on a 1734-OB8S - output data so you can turn the outputs on, and input data so you can monitor the card/outputs correctly to meet your required SIL/PL/whatever. The 1734-IB8S also uses two CIP connections
by default. Input data to read the inputs (and also monitor the the card/input status for safety validity), and output data so you can use your test pulse outputs as standard/muting outputs. This means that, assuming there were
only safety modules on your chassis, you could get a maximum of 10. However, if you don't need to use the test pulse outputs on the 1734-IB8S's in your program, you can set the output data to "none" for that card, and then the card only uses
one CIP connection, meaning you could put 20 1734-IB8S's on your chassis. The test pulses still work inasmuchas they provide test pulse functionality for your safety inputs - you just can't use them as outputs any more. Which is a small trade off to make if you're looking at maxing out your I/O rack otherwise. Technotes
65912 and
553849 (techconnect required for both) go over this limitation, or again, IAB will warn you if your configuration exceeds the number of CIP connections available.