I have an application requirement which demands that a Shutdown valve has to be actuated and the valve opening status has to be indicated in the Control room. The Control room is at a distance of 2 Km from the Shutdown valve. Can you provide a solution?

Following options were studied:

1. Energise a 24 VDC coil relay placed in a Junction Box 1000 metres away from the Control room. Finally energise the 24 VDC Solenoid vlave on the Shutdown valve at a distance of 1000 metres from the junction box through the 24 VDC potential free contact of the Relay. However, there is a chance of drop in the voltage causing unreliable operation.

2. Send a Analog current (4-20 mA) output corresponding to the ON-commnad from the DCS to the Local Control room DCS which is 1700 metres away. From Local Control room DCS, convert the Analog input to a corresponding Digital Output and energise the Solenoid valve of the Shutdown valve at a distance of 300 metres.

Does anyone have a better option?

 

Defitinely the last one, in my book.

If you are interested I have a very low cost solution, if you want to test it.

You can always contact me at [email protected]

 

If you've already got the wire in place, option 2 sounds very reliable, well within the capability of 4-20mA.

If you don't have the wire in place, consider Omnex wireless. We've put in several points over the past couple months and are amazed at how far apart the receiver/transmitter can be and how reliable it's been. Unlike 'radio' of 20 years ago. And it's industrial - DIN rail mount, 24Vdc power supply, good temp specs.

It's simple: DI's are dry contact in, DOs are relay, dry contact out.

At 2km, you might need a directional antenna, but we've got one pair at 1.5Km with the standard 1/4 wave omnidirectional antenna on unobstructed line-of-sight.

Bud

 

Reality check - the 1km roundtrip resistance of 1.5 sqmm wire is approx. 11 ohm - can you live with that? Check against the currents involved and the allowable voltage drop (a DC relay will pull down to at least 75% or rated voltage).

Meir

 

The solution will depend on what the control is switching on or off; right off, I think that the cheapest compromise solution is to use a small romote Control RS422 or RS485 module or some variation of that. You will also use something like 20AWG wire and to the PC side, you can use an RS422 to usb or serial converter or a plug in RS422 board. These modules are widely available and come with relays and digital I/O and or analog sensors on them. You select the one you need. Go to digikey for more information. The above solution can go up to 8000 ft.

Other variations include using an RS422 to fiber optic converter in between the control room and the device or even using a wires broad spectrum 2 way radio...

Good luck,

Walt Njuh
Akumeka Tech

 

Is it Hazardous area or Non Hazardous area?

It is possible to use I/O module with AI/AO or DI/DO with Modbus RTU on RS 485 serial bus with repeater, which would be interfaced with your DCS system.

other option is RS 485 to fibre optic converter,
which would allow you for 2 km of range.

Jari
[email protected]