Wireless Modbus RTU 2

[Keith1976]

Hi All;

I need some input here. I am installing drives in pump stations. Station A is located 15 miles from station B(manager office).

In Station A, there are 2 pumps with 2 drives (has modbus RTU built-in). At the moment there is no PLC orwhatsoever in station A.

Station B is luxury. It has 4pumps with 4 drives. Monitored and controlled by Honeywell HC900 via Modbus RTU, equipped with a 10" touchscreen. The manager is happy "enough". Out of contract agreement, yesterday he asked me to monitor stationA on the touchscreen. The customer is willing to purchase extra accesories/equipment.

Can anyone share me an idea on how to do this? Is there any assesories that will transform station A into a modbus slave as if station A is nearby station B.

Thanks guys...

Keith

 

[catserveng]

Take a look at the offerings from B&B Electronics, I'd start there.

Hope that helps.

 

[danw2]

If you were to wire Station B to Station A you'd run a long cable from the last Station B slave on the RTU line multidrop all the way to Station A, and then connect both Station A slaves 'in series' as multidrops. Take the wire away and you've got wireless, using a pair or radio modems.

Specifically, add a serial RS-485 Modbus RTU 900 Mhz freq hopping wireless radio as the master radio at station B. It becomes just another drop on the present 485 multidrop comm link. It does not need a Modbus slave ID number. The master radio will now see all the messages sent from or to the HC controller. The radio is configured for 'modem' mode, so it sends and receives anything that comes to its port. Hence, it will transmit/receive all messages on the link.

Then install a matching serial RS-485 Modbus RTU 900 Mhz freq hopping radio at Station A, and daisy chain the two Station A slave drives as multidrops. These drives will need different slave ID numbers that your station B's drives, let's say slaves 5 & 6 (assuming station A's
drives are 1,2,3,& 4).

Being Modbus, the slaves will only respond to the queries/commands addressed to them. Being Modbus RTU, there's only one master, so no collisions.

Configure the HC master to read whatever values it needs from slaves 5 & 6, tag the reads on the Modbus slave function block, use tags as needed for reporting on a screen on the O/I.

Be aware that the radio boxes are only a fractional part of a working wireless package. You need cables and antennae in locations where they can make a connection with enough signal strength to be reliable.

15 miles is a long shot for 1 watt unlicensed wireless (in the US).

Only consider frequency hopping technology. A freq hopper will have the punch-through ability that DSSS will not have over that distance. Do not use WiFi. Wifi is, by definition, DSSS.

You might find it worth it to obtain (might have to pay for) a 'software' survey from your wireless supplier over that kind of distance where you supply the GPS coordinates of the stations and the software looks at elevations between the sites and plots the 'envelope' (fresnel zone) of the wireless signal against the terrain elevation.

Even if the terrain is flat, you'll have to get your antennae up high for a long distance shot like 15 miles. You might need a tower. Use directional yagi antennae. Use low loss LMR400 antenna cable. Ground your antenna mast/tower. Spend the $300 per to isolate the RS-485

line out of each of the radios in case either radio takes a lightning strike, it'll save your drives and/or the HC controller port.

Lastly, be aware that although serial radios claim compatability up to 38.4 (or even 115k) baud rates, the serial throughput rates (through the ether) are on the order of either 9600 or 19.2k baud rate. The external serial line is 'hold and forward' internally in the radio. But for monitoring, that shouldn't be an issue for the small amout of data expected from a couple drives.

Honeywell has XYR 3000 wireless, Phoenix Contact has Data BD wireless. There are other brands.

 

[Keith1976]

Danw2,

Thank you for the enlightenment. At this moment I am waiting for the quotation from Honeywell and Phoenix Contact.

You are right, mostly the connection is for monitoring the remote station instead of controlling it real-time.

Rgds,
Keith

 

[Keith1976]

Danw2,

I got the quotation from Phoenix Contact and it costs me about EURO4500.

I am considering phone line now.

Keith

 

[itsmoked]

danw2; Great recipe++ !


Keith Cress
kcress -

http://www.flaminsystems.com

 

[cdevine]

Keith,

Danw2 is correct with his advice. The distance of 15 miles is a long way for unlicensed radios at 1W transmit power. Any trees, hills, dust storms, rain, fog and you might have some trouble getting a reliable link.

If you get a phone line you might be able to go for VPN solution or at worst data modems. You could even use reporting on exception rather than continuous connection. Do you have cellular communication in the area?

One often overlooked communication media is the gas/fluid that it is being pumped itself. For instance if Station A is upstream of Station B you have an idea whether station A drives are OK if pressure is within limits at the inlet of station B. Of course this communication method is quite a bit slower than radio but it is often a good and reliable solution as a redundant link.

Chris

Chris Devine

http://www.icande.com.au,

http://www.redbusbar.com

 

[Keith1976]

Chris;

GSM network is available. But is it reliable?

Keith

 

[cdevine]

Keith,

Whatever the link you go for you need to deal with the possibility that it will be intermittent or just fail. This involves knowing when it fails and having a course of action to deal with it.

You can use hardware fault status info or heartbeat strategies to know when it fails. A PLC is required at both ends for the heartbeat approach.

In slurry pumping projects we make the decision to go off solids feed but continue with liquid feed. To do otherwise we risk dropping below the settling velocity of the solids and blocking miles of pipework. Recovery of the link allows us to reintroduce solids.

This is why we have a main link in your case GSM but also use the process fluid as the redundant link.

Chris Devine

http://www.icande.com.au,

http://www.redbusbar.com

 

[Keith1976]

Thanks Chris

Keith

 

[YuriSarcas]

Is there a ability to run it through a server and you could go Ethernet? I have a site that has facilities in Arizona, California and Texas and they can see all of them on one computer.

I do not know the capabilities of the Honeywell controller.

 

[danw2]

The HC-900 controller is a Modbus TCP Master (or slave).

I'm not sure that freq hopping ethernet wireless would gain anything over serial radios, due to the power/bit factor decreasing with ethernet's larger packet size.

If the sites are internet connected, then ethernet would certainly be an option.

Dan

 

[Keith1976]

But too bad, there is no internet available.

Keith