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1791ES Safety Modules Frequently Asked Questions
Q: How many 1791ES modules can I connect to one 1756-ENBT?
A: There is no predefined number that can be specified. This number is application dependent based on multiple factors:
- RPI's , connection sizes, total amount of connections, other traffic etc.
- RPI's and connection sizes are application dependent and should be calculated based on safety reaction time defined during risk assessment.
Q: Why does one or more of my 1791ES modules keep giving spontaneous connection errors?
A: With Ethernet there are a large number of possible issues that may cause communication issues, including (but not limited to):
- Port speed/duplex mismatch on your network. It is advised to troubleshoot this by initially placing everything on your network to Auto Negotiate; ES modules, switch/hub, OITs, etc.
- RPIs too low. Try adding all ES modules in at default RPI and connection sizes to see if this helps.
- Out of connections or bandwidth on Ethernet gateway module. Check the 1756-ENBT/-EN2T web page to see connection status and CPU usage of the gateway module.
Q: What Ethernet resources does a 1791ES module consume?
A: The ES module has a capacity of 1000 packets per second (pps) for both safety input and a safety output connections (for a total of 2000 pps), and the module supports up to 5 safety connections (four safety inputs, one safety output). The controller that owns a 1791ES module will consume two of those: one input and one output connection per module.
Up to three additional controllers can make Input-only connections to that same module (the safety equivalent of a Listen Only connection, but with some important differences). Under the worst-case scenario of one owning controller and three listen-only controllers the module will be at its 5-connection limit.
Q: Does the Safety Ethernet/IP communication use Multicast traffic?
A: The module honours whatever is asked for in the FwdOpen connection request, whether the target-to-originator side is to be unicast or multicast. For planning purposes, the safest estimate is to allow for six unique multicast addresses per ES module, since each connection could be multicast on the T->O side.
Q: What is the difference between the Safety ES modules and their equivalent Safety DS modules?
A: Only the communication network. Internal operations are otherwise identical.
Q: Why can't I establish ownership to a my ES Safety Module?
A: The module may have been previously "owned" and must be reset to allow a new connection.
Q: I've added my ES safety module to the I/O configuration, reset ownership, and still I cannot get my safety outputs to come on!
A: Open the properties of the Safety DIO module in RSLogix, go to the configuration tab for the outputs in question, and ensure the configuration is set for something other than Not Used.
Q: Do all of the safety devices on my network need to have the same Safety Network Number (SNN)?
A: Absolutely not. In the case of DIO, the Safety Controller must know what the SNN is for all of the Safety I/O modules, but they do not have to match. In the SmartGuard this is done by establishing a Safety Connection.
Q: The User Manual shows two loads in parallel (Dual-load) across one bipolar output. Is this really legit? Can it actually be used in a Cat 4 system?
A: Yes. The whole purpose of bipolar outputs is to eliminate a single point of failure. Since a bipolar output breaks both the signal (P) and return (M) paths when off, there is no single failure that can cause both loads to be "stuck" on.
NOTE: While this configuration can be used in a system rated up to Cat 4, simply using bipolar outputs does not guarantee such a classification. There may be additional requirements that must be met for your application to reach the desired Category rating.
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