WEG CFW500 Safe Torque Off (STO) Part 1 from AutomationDirect

The optional safety module for the CFW500 drive has two motor-stopping safety functions. The first one is your standard Safe Torque Off which bypasses anything the drive’s control electronics is trying to do to the motor and directly shuts down the drive’s output. It’s the fastest and safest way to remove power from the motor so it can’t produce any torque. Hence the name: Safe Torque Off. But, there’s a problem with that. The drive now has no control over the motor and the motor is left to free spin down on its own, which is fine for some applications, but in some applications that could be dangerous and create a whole new set of safety issues. The good news is, the optional safety module for the CFW500 drive also has something called Time Controlled Safe Stop. Instead of simply releasing the motor to free spin down, the time-controlled safe stop waits for a time you specify before enabling STO and releasing the motor. That gives the drive time to safely ramp the motor down before releasing the torque. Of course, if the motor doesn’t ramp all the way down in the time you allocate, STO is going to kick in regardless and the motor will free spin down the rest of the way. For the safety nerds out there, here are the specifics. This is from the manual that comes with the safety module. In particular, notice that STO fulfills requirements for a Category 0 stop, and the time controlled mode fulfills the requirements for a Category 1 stop. The manual also has copies of the various declarations and certifications you’ll need. Having both of those options is a huge advantage of the CFW500 drives. And, since it is an optional plugin module, you don’t have to pay for it if you don’t need it. And remember – STO isn’t just for emergency shut down situations. For example, you can use a trapped key system or a safety gate to stop the motor via STO, work on your system, then re-enable STO when you are done. You didn’t have to stop the drive, remove power from the drive or shut down and restart any network communications to the drive. That saves you time, effort, and money. All of which is just one more reason the CFW500 drive is such a tremendous value. Let’s do a couple examples so we can see this in action. With the drive powered off, remove this jumper on top of the drive. This jumper shorts the STO pins so the drive is always active when the safety module isn’t installed, which means you have to have this jumper or the safety module installed to enable the drive's output. The latching tabs on the safety module hold it securely in place so you have to firmly press the safety module into the slot. There are two ways you can wire this up. You could simply take an ESTOP switch with two normally closed contacts and wire it directly like this. The problem is you have no way of knowing if these normally closed contacts are going to work when you need them. If they get stuck closed then when you hit the switch your system won’t shut down and bad things happen. It will probably work and for many applications that’s fine. But, if you need a truly safety-compliant system, then you will want to use an estop safety relay module. Why? Because it continuously tests the wiring and status of the switches so when you go to use them you can be assured they will actually do the job. And it allows you to add a manual reset switch because many safety applications require you to acknowledge the system is in a safe state before you can reset the ESTOP and allow torque to be applied to the motor. We’ll do the simple version in this video and then show you how to add the safety relay in part 2. I wired the normally closed contacts of the ESTOP to the STO module like this. The dual contacts are for redundancy – both have to be closed before the drive's output will be enabled. I used the 24 volt supply provided by the I/O module on the drive to power the safety module. I love that I don’t have to buy another power supply just to drive the safety module. Switch 1 tells the safety module we are using plain old dry contact switches to control it if both of these little switches are up. Switch 2 is used to set up the time delay – which we will do in the next example - so just make sure both of those are in the up position. Make sure the ESTOP button is not engaged and power up the drive. Press the Enter/Menu key and drop into the parameters group. Select that and scroll to Parameter 28. We see it’s a “1.” That tells us the drive sees the safety module. It’s a good idea to check that to make sure you installed it correctly. Hit Escape a few times to get back to the top level. Let’s try it. Hit Run and increase the motor speed. Hit the ESTOP button. Yep, we get the STO alarm code and the motor free spins down. Which with this heavy pulley, it’s gonna take a while. And most importantly the drive now has no control over the motor. I’ll release the ESTOP and now we can control the motor. Perfect. OK, let’s do that again, but this time let’s enable the time control. To set up up the time delay, both contacts have to be active or open so I’ll press the ESTOP switch to do that. We see the 160 alarm on the display telling us STO is active. Set both of Switch 2 switches to the ON position by pressing them down. The display changes to Alarm 162 to tell us we did that right. Press Escape, then Enter twice to get into the parameter menu. Scroll to Parameter 108 to enter the time delay. How long should this be? That depends on your system. I don’t have any load on this motor so I’m going to tell it to decelerate over 2.5 seconds so let’s give it a 5-second window to do it in just so it’s real obvious in our demo. Enter a 5-second delay, enter to accept. The flashing display is telling us we need to verify this by going up to Parameter 109, and press Enter to accept that value. That’s just forcing us to make absolutely sure that’s the time window we want. The display stops flashing to tell us we are done. Move both of Switch 2’s switches back to the Up position to end the setup. Finally, we need to tell it how fast to decelerate the load. That’s a special decel ramp that’s in Parameter 106. We wanted that to be 2.5 seconds. Enter to accept. Escape back to the top level. To recap, we expect to hit the ESTOP, see a linear decel over 2.5 seconds, and then at the 5-second mark STO should kick in. Let’s try it. Release the ESTOP contacts. Hit Run and let the motor spin up. I’ll hit the ESTOP switch, we see Alarm 161 telling us we are in the time delay ramp-down portion and a couple seconds later we get Alarm 160 telling us we have switched over to STO mode. Since the motor is already stopped, it has no effect. So, let’s do that again but this time, let's tell it to decelerate over 5 seconds, but have STO kick in at 2 seconds. The ESTOP is already engaged and we see the 160 alarm so we can skip that step. Both switches down. Go to Parameter 108 and set the time delay to 2 seconds. Go to Parameter 109 and confirm it. Backlight stops blinking. Put both switches back. Go to Parameter 106 to set the decel time to be longer than the STO cutoff – 5 seconds. Escape twice back to the top level. Release the ESTOP. Hit Run. Remember – we expect to hit the ESTOP, deceleration should start, and STO should kick in before it's finished. Here we go. ESTOP. Alarm 161 tells us we are in the timed portion and then around 2 seconds, it switched to STO mode and the motor was left to free spin down. Perfect. One caution: you have to complete the programming portion – the time while both dip switches are down – within 2 minutes. If you don’t the display will return to Alarm 160 and you will have to power down the drive, put the switches back up, apply power to the drive, and start all over. To summarize: we set up the drive to have its output power cut off when the ESTOP button opened its two switches in both STO mode and the time-controlled mode. Remember, when using nothing but dry contacts you have to assume the ESTOP switch is going to work. In many applications, that’s not good enough for a fully compliant safety system. Join me in Part 2 where we’ll show you how to use a safety relay to build a proper safety system. Meanwhile, click here to learn more about the CFW500 family of drives. Click here to learn about AutomationDirect’s free award-winning support options and click here to subscribe to our YouTube channel so you will be notified when we publish more videos like this one.