"T" Terminals on a Safety controller

theColonel26

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So this is an example safety circuit for a Yamaha RCX-340.

I am wondering what the T terminals are on the example safety controller? are they just a V+? Can they be substituted for a 24VDC Hot? See attached picture.


For the record I am using a Banner SC-26 for the Safety Controller.

CTRLS-SB-BEN 2018-1031 11-37-59.png
 
Last edited:
Test pulse outputs can be used to detect an unexpected change of voltage. They send very low signals (so as to not actually trigger the output) to continuously make sure that the output channel is functional.
 
As the people above have mentioned, they are test pulses. You cannot substitute 24VDC; that's exactly their purpose.

A test pulse is usually 24VDC, but it contains a pulse pattern. Each test pulse has a different pattern. T0 might have a pattern where it's 24V for 50ms, 0V for 2ms, 24V for 50ms, 0V for 2ms, repeat. T1 might be 24V for 40ms, 0V for 1ms, 24V for 40ms, 0V for 1ms, repeat.

The idea is that when you configure your inputs, you tell them which test pulse they're supposed to be wired to. To turn the safety input on, it needs to see that same test pulse pattern. If it sees a different pattern, it knows there's a wiring fault and turns the input off. If it doesn't see a pattern at all, it knows you've shorted 24V to the input and turns the input off. Basically it's about detecting wiring errors, short circuits, wiring faults, etc etc.

Now, there are some devices that you can't use a test pulse. Light curtains, for example - they've got their own smarts internally and just turn on two OSSD's, which are just straight 24VDC. No pulse. So in that case, you wire the OSSD's to your safety inputs and configure the safety inputs to not use a test pulse. You no longer have the short circuit or wiring error detection - but you don't need them, because the light curtain itself does that. Again, it has its own internal smarts and will perform its own cross checks on its outputs. If it detects a fault, it'll turn off both OSSD's.

TL;DR: run all "dumb" safety input devices off a test pulse and configure the safety inputs for the correct test pulse. Run all "smart" safety input devices off 24VDC and configure the safety inputs for no test pulse.
 
To my understanding, any Dual-Channel configuration with integral monitoring, or using input-connected test pulses is rated as a Category 4 safety circuit, according to the Banner SC26 Instruction Manual (p.83) :

Banner-Categories.png


Each Input in a dual-channel should ideally have its own test pulse. Connecting both inputs onto the same test pulse could result in "false positives" in case of a short-circuit between T0 and T1. Ideally (but not necessarily, depending on severity of application) it would look like this :

Cat4-Config.png


You mentionned you use a Banner SC26, but I'm guessing your drawing isn't directly representative of the device? To my knowledge they don't use T# nomenclature for test pulses. They use configurable IOs instead, and have 2 dual-channel safety outputs SO1 & SO2. Your drawing looks more reminiscent of a Pilz SC.
 
To my understanding, any Dual-Channel configuration with integral monitoring, or using input-connected test pulses is rated as a Category 4 safety circuit, according to the Banner SC26 Instruction Manual (p.83) :

Banner-Categories.png


Each Input in a dual-channel should ideally have its own test pulse. Connecting both inputs onto the same test pulse could result in "false positives" in case of a short-circuit between T0 and T1. Ideally (but not necessarily, depending on severity of application) it would look like this :

Cat4-Config.png


You mentionned you use a Banner SC26, but I'm guessing your drawing isn't directly representative of the device? To my knowledge they don't use T# nomenclature for test pulses. They use configurable IOs instead, and have 2 dual-channel safety outputs SO1 & SO2. Your drawing looks more reminiscent of a Pilz SC.


No the example drawing was from the Yamaha RCX-340 Instruction manaual. I do not know what model they are using for the safety controller in the example. I plan on using the SC-26. But I do not need Cat 4. It is a tiny robot in a physical enclosure. I am just trying to better understand safety categories. I plan on using a 2 terminal dual channel configuration for everything (right now anyway). I am working on a set of example schematics with different configurations and I going to start a new thread for that. (Shortly)
 

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