Help me (please) wire up my flame detector

Palak · Oct 4, 2021

I want to wire into a CNC grinder a flame detector into the e-stop circuitry, such that when a flame is detected it shuts the grinder down and stops coolant flow.

The e-stop on this machine is a NC (normally closed) circuit, as per usual according to my understanding. We have a fire suppression system wired in, such that when the extinguisher goes off, it creates an open circuit, triggering the e-stop. We want to do the same thing for the flame detector (this is for redundancy).

The flame detector we have is a Det-Tronics PM-5MPX -- a detector commonly used in machining, according to their marketing materials. The wires into the detector are input power, power return, and 4 alarm out wires, as well as 2 trouble wires. So, the alarm switch appears to be normally open.

With the fire suppression, it was easy -- we have a single switch at the extinguisher, which is closed (held closed by the extinguisher pressure). We simply wire both ends of the switch in series in the e-stop circuitry.

But, I don't understand how I can incorporate the flame detector. In series, we would have a 24DCV input from the estop circuit, the return back to the circuit, but how do I get the alarm-out signal to create an open circuit when the flame detector is triggered.

FYI, the detector is potted, so no possibility of changing anything with the detector.

I am currently talking to "customer support", but they don't seem to know a lot about the product.

Would appreciate any thoughts.

atomarc · Oct 4, 2021

I have absolutely no clear picture of what you're describing so this post may be fake news, but a simple relay with a coil voltage to match your system will allow a simple a NO or NC switch closure to achieve what you're after...I think.

Stuart

JST · Oct 4, 2021

If it does not have an "NC" contact, that makes it more complicated. And I don't care for that sort of device, because a complete failure to operate looks the same as a "no flame" condition.

You could add another relay, which operates when the flame sensor detects flame and closes its contacts. That added relay would have to supply the NC contact, and open it when the detector shows a flame detected.

Just a Sparky · Oct 4, 2021

Does this help at all?

https://www.det-tronics.com/Content/Documents/PM-5MPX-Instructions.pdf

There is an appendix with a few wiring diagrams.

Palak · Oct 4, 2021

Yes, those are the instructions that we have. But, they don't seem to get us where we need to be. At this time, customer service is of little help.

JST, thanks for your reply. This detector does blink once every second, showing that it is operational. Do you have any recommendation for the type of relay (a McMaster Carr link or other showing what you have in mind?)

Same for you Stuart. What type of relay should we be looking for? What is a good search engine string I could use to self-educate on this problem?

Thanks again for the replies.

JST · Oct 4, 2021

I would have, but the instructions are more confusing than your description! You are using it differently than their diagrams.

The relay should be rated to operate on the DC voltage you have available going to the detector, and the relay coil should take less than the 100 mA they state as the rating of their internal circuitry.

The NC contacts of the added relay should be in series with the e-stop circuit.

Palak · Oct 5, 2021

Yes, I think the detector/sensor is really designed to work in conjunction with an alarm system, but we are wanting it to trigger our e-stop.

I am researching relays, but it seems to me that there will be 3 inputs/outputs? One into the system of 24VDC, one out at 24VDC at its NC condition to keep the e-stop from triggering, and a third input from the alarm wire, which when at an alarm condition will be at 24VDC which will trigger the relay to an open condition, and causing emergency shutdown? Let me know if that is how it would be wired, as I have never dealt with a relay before.

Is there an online vendor that I could call to get some help with this in specifying a relay?

Thanks again.

corednc · Oct 5, 2021

You actually have 2 problems, the normally open output and the max current of 100ma on the output.

I will try and make this as simple as possible.
Go to ebay.com and get a 24V relay module, here is a link for one of many.
2 Channel Low level trigger Relay Module 24V | eBay

Connect 24V to VCC and ground to GND as indicated, then connect alarm + to IN1 on the module and alarm - to GND.
Connect your estop circuit to the normally closed output on the K1 side of the relay (Note IN1 for K1, IN2 for K2).

sfriedberg · Oct 5, 2021

Just to expand on that slightly. Use the NC contacts of the relay (two wires) in the emergency stop series. Use the flame detector output to drive the coil of the relay (two wires). The flame detector is not connected directly to the emergency stop. You want a "signal" relay, not a massive motor contactor. Pick a relay whose coil requires less than the 100mA limit of the flame detector output.

Froneck · Oct 5, 2021

Having worked for quite a few years as a Fire Protection Engineer I'm familiar with how system detectors work. All System detectors are open circuit. Alarm is detected by the control panel when line is shorted, that is a contact closed or solid state component conducted. That is for Smoke, Flame, UV and thermal detectors. Manual Fire Alarm pull stations are simply a NO switch that closed upon activation. So that wiring problems could be detected a small current was passed thru the wires having a resistor at the end of the line, some fire codes required the resistor to be in the control panel so then 4 wires were used, 2 out and 2 back. I'm not familiar with the flame detector you listed, I have been out of Fire Alarm for many years. The one we used was by Pyrotronics considered the best there was. Simple connection to a relay is OK if as you mentioned it is simply a redundant signal however Flame detectors can be quite sensitive to Sun Light.

Palak · Oct 5, 2021

Thanks very much, Corednc.

I think I understand everything you're saying - I will later post a schematic to make sure I've followed everything.

I think that the detector needs to be powered by 24VDC, which I think should be supplied by the e-stop circuit. Do I run power and power return direct from the circuit, or does it need to go first through the relay?

Also, not sure I understand your statement "(Note IN1 for K1, IN2 for K2)."

Thanks again.

Palak · Oct 5, 2021

Thanks. But per my last comment, I need to supply power to the detector, which I was planning to do through the e-stop circuit.

sfriedberg · Oct 5, 2021

I'd strongly encourage you not to take detector power directly from the e-stop circuit. If the e-stop series is connected on one end to a 24V source, then run a separate wire from the 24V source to power the flame detector. Don't just add a tap somewhere along the e-stop series.

Palak · Oct 5, 2021

Thank you. Can you explain why?

Also, in your first comment, I'm not sure if you are disagreeing with the linked ebay relay. Did you see a problem with utilizing that relay?

Thanks for your help.

corednc · Oct 5, 2021

As sfriedberg said, don't take the 24V from the estop, it is a safety and function issue. If you do then when an upstream device opens the estop circuit, power to your flame detector will be cut which is a safety issue. You do not know the current rating of the other devices on the estop circuit so powering your flame detector and relay module from the circuit could cause too much current draw and damage the other devices.

Yes, find a 24V power source on your machine and run a wire from there, the wire will run to both the flame detector and the relay module, in this case order does not matter.

The linked module has 2 relays, if you look at the picture the inputs are labeled IN1 and IN2 and the relay outputs are labeled K1 and K2. I was saying that you should make sure you connect the right output to the right input.

Palak · Oct 5, 2021

I apologize if I sound dense, but I don't think I understand (if you can't tell, I have unfamiliar with relays.)

I think the concept of the relay is to be a closed switch in the e-stop circuit, and to open when the alarm signal makes the relay become open, thereby activating the stop and shutting the machine down. It sounds like IN1 is an input to the relay, and K1 is the corresponding output. In order to be integrated into the e-stop circuit, the 24VDC e-stop voltage must pass through the closed relay. BUT, my understanding of what you wrote seems to be that we need to put a separate 24VDC line into the relay? Where and how then is the e-stop circuit going through the relay?

Your help is much appreciated.

corednc · Oct 5, 2021

Yes, you need to put a separate 24V line (separate from the estop wire) into the relay module and the flame detector. Look in the electrical cabinet or the wiring diagram for your machine and you will find that there are connection points for the 24V power supply from which you can run 2 wires, one at the 24V terminal and one at the ground terminal. These wires will go to 24V and ground on the relay module and flame detector.

You should go with this module because it is a single relay and all of the connections are labeled so it is less confusing. It also has screw connectors on both the input and output to make it easier to connect the wires. Make sure you select the 24V version when purchasing.

HW-803 1 Way Relay Module w/Optocoupler Isolation High Low Level Trigger | eBay

So if you get that module then these are the connections you need to make

ESTOP+ -> RELAY MODULE COM
ESTOP- -> RELAY MODULE NC

24VDC FROM MACHINE -> RELAY MODULE DC+
GROUND FROM MACHINE -> RELAY MODULE DC-

24VDC FROM MACHINE -> FLAME DETECTOR 24V (V+)
GROUND FROM MACHINE -> FLAME DETECTOR GROUND (V- / POWER RETURN)

ALARM + FROM FLAME DETECTOR -> IN
ALARM - FROM FLAME DETECTOR -> DC-

Palak · Oct 6, 2021

Thank you so much, Corednc. I already ordered the other relays, but will order this one as well. These relays are really economically priced. I wish all electrical stuff was this affordable.

Since I already ordered the other relay, can you tell me what is the name of the female square connectors that are used to attach to the single male connections on the relay board (in case I decide to use them.) What gauge wire is typically used in a 24V relay board?

Thankfully, this is a project that we can test easily -- once installed, simply flick a bic in front of the detector, and see if the e-stop is triggered.

Thanks again, and thanks to everyone here contributing your expertise and ideas. Very much appreciated.

corednc · Oct 8, 2021

The relay module consumes probably less than 20mA given the relay consumes approx 15mA max at 24V and I think the flame detector consumes 10mA. So you can use any wire gauge you can easily handle. Keep in mind that your e-stop wires may have a minimum gauge. I would use something around 24awg for everything.

The connectors are generally called "dupont connectors" I forget the real name, but an ebay search for them will bring up many choices. If you don't have the correct crimper it is easier to buy pre-terminated wires and then cut and crimp on additional wire with a butt splice.

Froneck · Oct 9, 2021

I don't know how important it is that the Flame Detector work as intended to shut the system down. As I mentioned I was a Fire Protection Engineer for quite a few years, any system has the connections supervised so that if a wire breaks there is notification. I know the wire length is not as long as it is in a building fire alarm system but you might want to include circuitry to determine if the flame detector is getting power and the wires needed to shut things down will work when needed. Some of our systems were quite short, Fenwal Halon release was done with blasting caps that were wired in series. A small current was run thru the blasting caps to be sure they were connected when needed.

Help me (please) wire up my flame detector

Aluminum

Diamond

Diamond

Hot Rolled

Aluminum

Diamond

Aluminum

Aluminum

Diamond

Titanium

Aluminum

Aluminum

Diamond

Aluminum

Aluminum

Aluminum

Aluminum

Aluminum

Aluminum

Titanium

Similar threads