Hi,

Can somebody clarify the following.

Existing facilities have been installed with 3 wire flammable Gas detector (MSA make. We want to connect this detector to the safety ststems like Triconex, FSC etc.

Whether somebody came across this situation? and how was it resolved? Do we have install any intermediate electronic block to connect to Safety system input cards?

Response on this is appreciated.

 

Vadooth,

In all probability, your 3-wire gas detector is a catalytic type, which forms one half of a bridge (one leg being a pellistor and the other a resistor). Normally this would be connected to a module that has the other half of the bridge.

Most Gas Detector manufacturers have a 4-20mA transmitter that can be used to interface to a PLC, for instance. It's also possible that you already have a 3-wire 4-20mA transmitter built in.

You would need to provide more information for further help.

 

What type of output does the unit have?

Did you try contacting the manufacture for technical specifications?

What type of input power does it require?

Going to need more information before I can tell you how to connect the device.

How about a MSA model number?

The device could have a dry contact output, it could have a voltage or current output. Most the gas detectors I used, were powered by 120vac or 24vac or even 24vdc. They all provided a dry contact output.

I suggest you look up the data sheet for the device, do some reading on how to connect it properly and make sure it is compatible with your input card.

MJH

How are the others connected?

 

Ok Friend this is what you have to do.

The MSA Combustible gas sensor, should generate its own current loop (4-20 mAmp), that's wy you have 3 wires ( 24vdc+, 24vdc- & signal ). The safety system should be able to read the current loop. Then it also should be programmed to activate on pre alarm & alarm by the % of LEL of the gas to be sensed.

A good guide to this connections are the Detronics.com site and find the data sheet & manuals, it is not MSA make but will give you a good idea.

We area a safety company in Venezuela and make these type of integration all the time for the oil companies.

Saludos

Luis F. Herrera

 

Best solution is to use MSA Suprema system where you can use your 3 wire gas detector directly.

 

Typically, EExd detectors require 3 wire as the power needed is more than what 2 wire can supply. These are e.g. catalytics or Infra-red. The 3 wires are Power (24VDC typically), Common (0V) and Signal (4-20mA). On PLCs, or I/O cards that do not support 3 wire, you need to use a separate power supply , preferably from the same PSU to the PLC (common ground), to give the extra juice. Hookup that 24VDC connection to this and that's it.

Uh... Im with Draeger.

 

You are very correct. Half of the wheatstone bridge circuit is located in the control unit.

Thank you all for your response.

The detector model was MSA 410-PRP (Pellister type). We could get a wheatstone (Catalytic) to current convertor card (system 54)from Zellwager which takes four detectors (Catalytic wheatstone type) input and provide four 4-20 mA outputs which we will connect to the PLC Analogue card.

Once again I thank you all for the fast response.

Regards,
S.Vadhooth