text: <s>[INST] PowerFlex 525 Safe-Torque and Run input Summary: STO and Run input timingI have a very simple machine with only push-buttons, relays and an old PF70 drive. We wish to at least upgrade the safety on this machine and want to use the 525 and its STO. My concern is the timing of the run and STO inputs. The simplest way to do this is to give the run and STO, using safety relays, at the same time. Will this work or will these signals being so close together cause an issue? [/INST] https://literature.rockwellautomation.com/idc/groups/literature/documents/um/520-um001_-en-e.pdf If you would, look at page 241 of the attached manual. If you're using an MSR - MONITORING Safety Relay, then the safety action comes from some sort of guard switch or e-stop button. The start button does not go through the MSR at all. If this is your intent, you will have no problems with timing between the start ant STO inputs because the STO input has to be made before the drive will even look at the start input. However, your description makes me think you're going to replace regular ice cube relays with these: https://ab.rockwellautomation.com/Relays-and-Timers/PCB-Pin-Style-Safety-Control-Relays And try to send both the start signal and safety signal through these to the start input and the safety input simultaneously. In this case, you will likely have a timing problem. In addition, you will not materially improve the safety of your machine. These ice-cube style relays are intended to have both of their channels used in parallel. Their contact pairs are force-guided - that is, the contacts are mechanically attached so both must make or neither does. Your simple machine probably uses only one contact of a regular relay, so adding in a safety ice cube relay without rewiring into 2-channel circuits doesn't add to safety at all. \\n </s>