Sensor outputs in series without relays.

Hey Fellas,

I am trying to wire up 4 different sensor outputs to a VSD to issue a stop signal on detection of an obstruction. The application is a turntable and the sensors are proxy sensors with 4 meter range, so the idea is to stop the Turntable on detection of an obstruction on any one of the four sensors. I am using the Run enable function on the DI of the VSD (OMRON 3G3MX2) and cant use four different DI's for the four outputs of the senors.
My question is to how to wire up these outputs so that I can use a single IP on the VSD.
I don't have enough space inside the control box to use relays in series. So relays are out of questions.

Thank you.

Can the sensors be setup to be normally closed? If so you may be able to wire the sensors in series like you would a hard wired stop circuit.

Will.

willxfmr said:

Can the sensors be setup to be normally closed? If so you may be able to wire the sensors in series like you would a hard wired stop circuit.

Will.

Click to expand...

Thanks for the quick reply Will!

Yes the sensors can be set to normally closed (I've used NC to put them in series with relays, to use the run enable function on the VFD in the past projects).
What do you mean when you say hard wired stop circuit.

Cheers!

In normally open mode, add a series diode to each sensor output. 1N4004.
+ lead of sensor to Anode. All 4 Cathodes to the single point on the VFD.

Be sure to check the allowable current draw for the sensor can handle.

Sending the signal to the drive thru a single sensor's contacts would probably be fine but if there is any load associated with having four in series plus the load of the drive's input then it may add up.

Better safe than sorry.

There are DIN rail mounted relays from several manufacturers (Phoenix, Eurotherm, Finder, etc.) the don't take up any more space than a terminal block. They should allow you to do it the right way.
If you don't have room for those relays in the enclosure then you should take a serious look at the cooling requirements for the 3G3MX2 drive.

find a sensor c/w relay NC

Those terminal strip sized relays mentioned by mendonsy are an excellent solution when you have minimal space. I have used them before.

The only downside is that some of them make it harder to replace the relay contacts without rewiring, so I would check that when you spec the parts.

Here is a basic schematic of how you could wire it up. This is assuming that the sensors outputs operate in the same way that a simple relay does and that the input for the VSD operates as a closed contact input. What I believe Kulga… (kinda a long handle don’t ya think?) is saying is that most VSD’s (and VFD’s) have an emergency stop circuit that must be a closed circuit for the drive to run. In this drawing if anyone one of the sensors goes open the whole circuit is open thus the drive stops.

It is worth pointing out that it would be better to use a “run” input that starts the drive when closed and stops it when open rather than the E-stop. The E-stop should be dedicated to its intended purpose plus some E-stops require that some sort of reset be done if activated. If you do use the E-stop input make sure that there is still an E-stop switch in series (it would be like a fifth relay).

kulgauravkanade said:

I don't have enough space inside the control box to use relays in series. So relays are out of questions.

Thank you.

Click to expand...

I don't know your space budget, but there are multi-relay modules that are small.
This model is 34mm wide X 84 mm tall.
The relays are single N.O. and are replaceable with the included tool. It has two 4-position jumpers.

Firejo said:

What I believe Kulga… (kinda a long handle don’t ya think?) is saying...

Click to expand...

So I got the name wrong. Sorry Willxfmr and Kulga...

Interesting..

Guys I really appreciate the help here! Such an amazing community!
Alright, this is what I've done.
Using keithkyll advice I am using diodes at the sensor output, (NO sensor output).
The VFD is set on a command called 'Permission to run' (the respective input is set to NC).
Thus, when there is no obstruction, there is no signal on any sensor output, and the VFD permission to run is NC, allowing me to run the VFD (Forward- Reverse) as soon as any one of the four sensor detects an obstruction, the NO of sensor closes and NC of VFD opens thus cancelling the permission to run.

Guys, I know there are relays the size of terminal strips, but I want to avoid using them , I wanted to design a logic which will let me use a single DI on the VFD without using multiple relays.

Firejo, Chris Hasler, mendonsy and dogleg43 thank you so much guys. I really appreciate your help.

Cheers!