Matt, sorry for the delay in getting back to you. Timbert has kept you well informed, and I see you are reading up on safety functions, good.
You've had a eureka moment, but I think we need to hit the brakes here.
milmat1 said:
And again had a risk assessment been done this would have all been apparent as well..
No risk assessment?
We want to help you Matt, but you have to remember this is your safety design and it will be your responsibility once it's a reality. So it's very important you understand what you are doing here, and why. Don't proceed with installing anything until you are fully aware of all the necessary requirements to meet the risk assessment that should be carried out. It should have been done before any safety components were even selected.
If you don't have a risk assessment Matt, what are you basing your safety measures on?
Was/is someone else over this project that has handed it over to you? If you are not able to risk assess this yourself Matt, someone who is trained to do so will have to carry it out, but it should be done.
Learn about the do's and don'ts first, then consider tackling an actual safety project. You're playing catch up here, but take your time. Don't be too willing to put your head on the block if you are not up to this just yet. I'm not trying to frighten you here, I'm just fore warning you in case of repercussions down the road.
If there is no immediate rush to do this project, then we have time to help teach you first.
We'll start with the safety relay you have to play with. The MSR138DT. I've attached the basic wiring diagram with colour coding so we can refer to it.
I wont refer to safety terminology such as PL, SIL, Stop Category, etc. any more until you're happy with how the safety relay works.
I'm going to break it down for you the best I can, and forgive me if you're already beyond some of what I'm explaining, or I'm repeating anything others have already written.
A safety relay is basically a logic solver with built in redundancy and self checking measures. It monitors one, or two normally closed input channels, depending on the level of safety required. This is usually referred to as single or dual channel. Dual channel, as mentioned earlier, provides double redundancy in the input checking circuit.
If using dual channel and one or both channels open circuits, the safety relay trips it's output channels.
The safety relays output channels can be tripped instantaneously or delayed, or have a combination of both, depending on the level of safety required. The duration of the delay should be determined by the required safe stopping time of the function controlled by the safety relays outputs.
Again, depending on the level of safety required, the safety relay may be automatically reset as soon as the input channels are closed, or manually reset using a reset push button, after the input channels are closed. Or manually reset, with monitoring of the output circuit, after the channels are closed and the output feedback circuit has closed.
Here you can see the MSR138DP has two safety input channels.
Channel 1 = Green S11,S12
Channel 2 = Orange S21,S22
These are used to monitor the safety equipment that can trip the safety relay. As Timbert mentioned, these can be any safety protection measure such as emergency stops, guard interlocks, trapped keys. Also electro-sensitive protective equipment(ESPE) such as light curtains, photoelectric switches, laser scanners and even cameras.
On this relay, as with many others, it monitors for cross faults on the two input channels.
The emergency stop has two normally closed contacts to wire the dual input channels through. So channel one goes from S11 through an emergency stop contact and back to S12. Channel two goes from S21 through the other emergency stop contact and back to S22.
S11 is a source +24VDC, so it loops to S52 to provide the +24VDC needed internally for channel two. S21 and S22 are switching -24VDC.
So on the MSR138DP, channel one switches +24VDC and channel two switches -24VDC. It's important to know this when fault finding input channel loss problems.
The reset, in Blue, can be any normally open Blue momentary push button. You wire the normally open contact from S33 and back to S34.
This relay differs from the one I posted earlier in that the reset and output monitoring is done separately. Here the output monitoring is done from Y1 and Y2, in Grey. If the manual reset is pressed, the internal logic checks if Y1 and Y2 are closed and if so, enables the reseting of the safety relay.
If a reset is attempted while the delay time is still active, the relay will not reset and will go into lockout. After the delay has timed out, you have to cycle the safety inputs, e.g. latch and unlatch an emergency stop, and wait for the delay to time out again before attempting another manual reset.
Note: this example shows the output monitoring wired to the normally closed feedback contacts of K1 and K2, in Brown, which are controlled by the two instantaneous safety outputs 13,14 and 23,24, also in Brown.
D1 and D2, in Yellow, are controlled by two of the three the delayed safety outputs 37,38 and 47,48, also in Yellow. Note: D1 and D2 are not wired for output monitoring.
57 and 58, in Pink, are the third delayed safety output, which can be wired to a PLC input for monitoring of the safety relays status.
Notice how all five of the safety outputs show dual internal contacts. If any one contact of any output fails closed, the other contact should still open, maintaining the safety function. This is double redundancy to bring the safety function of the relay to a higher level.
I think that's enough detail on the safety relay for now.
Are you happy enough yet as to how you would need to wire it all up?
milmat1 said:
I have 7 MOVAXIS drives. and two MC07B VFD's so
7 MX80A's are 7 @ 950mw = 6.7W
+
2 MC07B VFD's @ 7.5W each = 15W (don't know why so high??)
so 21.7W total. At my 24VDC that is only 905 ma. So my 3 amp safety relay contacts are good
Your MOVIAXIS should be MXA
81A's, not MXA80A's.
MXA80A's are standard with no STO.
MXA81A's have one STO coil and feedback contact.
MXA82A's have two STO coils and feedback contacts.
The MOVITRAC MCO7B's have only one STO coil, no feedback contact.
I'm assuming you want to drive them all to a safe stop, but be sure that the delay you think you need, and it's duration, is required and safe to implement across all seven MOVIAXIS and both MOVITRACs.
The reason the MOVITRACs STO relay coils are 7.5W each is because they are size 3 drives. The STO safety relay also supplies the DC into the drive for the output section. So this relay is larger to facilitate the required larger DC supply.
Note: Because the MOVITRACs do not have an STO feedback contact, you will not be able to series the output monitoring circuit through these as well as the seven MOVIAXIS.
SEW also recommend that, once you have more than eight drives in group disconnection, you must wire a flywheel diode across each STO coil to protect the main safety relays output contacts.
Although the MSR138DP's safety outputs are rated for 3A/24VDC inductive, they recommend 6A slow blow, or 10A fast acting fuses upstream of the output contacts.
I'd look into that risk assessment ASAP Matt. If you need any help with that let us know.
p.s. A belated happy 50th!
G.
"If you think safety is expensive, try having an accident".
