SLC 5/0x and Radio Modems


Thread Starter

Townsley, Bill

Hi all, I think this question might have been posted in the past. I looked through the archives and found some stuff on the topic but not everything... I have an application that 'requires' monitoring several remote storage tanks. At each remote site there is only one or two points that need to be monitored (level). I would like to use something like a spread-spectrum radio modem since it would not require a licence and there is not necessarily any power, let alone telephone, in the tank location. These tanks are regularly moved to different parts of the fields as well. In other words, the cost for a hardwired system would be too expensive to maintain. The distance to these tanks is generally less than 10 miles. Total number of remote sites will probably be less than ten. I was figuring that I would need a solar cell type installation since there would not be any power available. The level reading need not be continuous, rather, it can be on a regular polled basis - perhaps once or twice a day. However, it would be nice to have the remote transmitter send a logged history of the level. That is, log the continuous values but only send the stream to the PLC twice a day. The monitoring PLC will be either a SLC-5/05 or a SLC-5/03. Any suggestions on what to do. I have never done anything like this, so even the most basic help would be appreciated. Also, what ball-park costs do you think would be involved? Currently, there is a person that drives around once every couple of days to check the tank levels. If the 'automated' cost is less than the 'manual' cost then I can justify installing the system. Thanks for any advice. Bill Townsley
Hello Bill 1: We build an RVI (remote visual indication) unit that can be bolted to the outside of a tank. A magnetically equipped float travels inside the tube. A row of flappers of flags is attached to the outside of the tube. As the float moves it rotates the flags thus changing the color - thus indicating level, safely. Level switches or our continuous probe can also be attached to the standoff as well to indicate level electrically. They are activated by the same float as well. 2: Switch points are SPDT and supply contact only indication - so low voltage will work. We can supply solar power unit as well. 3: Our continuous model can run on a 9 VDC battery so a solar device would power it. Normally it has 4 - 20 output or 1 to 10 VDC resistive chain. 4: We have a 7 day recording chart that is 9 VDC as well - mostly for temp - but we can convert that to level. 5: We don't make a signal sender for over the air waves but I am sure a product is available to convert our type of simple signal. Some information is on our web page at: Thanks Bob Hogg Almeg Controls PS - Controls are also available for internal mounting. Note - We are closed from April 13 to 20th.
I have used spread spectrum modems by Bentek Systems ( The modems have limited I/O built in to the modems (4DI/AI and 4DO. I think these modems only have Modbus protocol. I was using a Modicon PLC to do all of the polling of the remote tanks.
The ten mile range might give some problems for unlicensed radios, even the spread spectrum versions. Take a look at FEDD Systems of Houston, TX for some equipment which just might do the trick. (i think). John Beck Pennzoil Quaker State Refinery Shreveport, LA (for now, at least) e-mail johnbeck

Toni Kaesbeck

Bill: Measurement on the tanks depends on tank type, accuracy asked for, product stored. Options available are - float&tape gauges (e.g. VAREC: mechanical, power supply for transmitter only) with transmitter, - radar - servo gauges Connect the gauges via a RTU with MODBUS (RS-485) on a radio modem to the PLC. The whole system powered by a solar panel, backup batteries. You need to define the length of backup time, location, average sun shine duration for configuring the batteries and panel size. Power requirements depend mostly on power consumption of the gauge: Low for float and tape, higher for some radar and servo. Check Please contact me, if you need more information! Best regards, Toni Kaesbeck

Ali Khorramshahi

Bill, Motorola's MOSCAD family of product is a PLC/RTU/Telecommunication Gateway. It is a proven platform for deploying wireless data acquisition networks. I apply Motorola's MOSCAD and MDS Spread Spectrum radios to systems that have the same requirements as your application. The MOSCAD-Light works very well with solar power. The following web site provides you with more information relating to this product. Ali Khorramshahi DigitaLogic, Inc. 3600 Clipper Mill Road, Suite 211 Baltimore, MD 21211 Tel: 410-662-9500 Ext. 102 Web Site: email: [email protected]

Techno Socrates

I know of one "official" company that has the insurance of making your application work with the A-B platform. They are license free radio modems from data-linc. As for the price, I would guess more than 1500$ each. They are industrial modems...? I know they work in multi drop for the ethernet one but for the rs-232 one, I am not sure. I think they are developing or they are selling now, some sort of digital and analog modems...i.e. on one side you have your input or output plc card connected to one, and your devices in the field connected to the other one. their site for the specs of these modems is the following: I hope this helps

amora fibrianto

try to download scada application guide from ab website, they're good starting literature for ab scada application. i've done remote monitoring with ab slc5/04 and mds modem with about 20 km distance (but it wasn't spread spectrum one)....mds( also produce a spread spectrum radio. can't remember which one. try also both are ab encompass partner.... regards, AF

Larry Taylor

We manufacture a battery-powered, intrinsically safe tank overfill protection system called FillCheck®. No solar needed, this 900 Mhz frequency-hopping system operates on a user-replaceable Li-ion battery for 2-3 years, and even notifies the operator when the battery needs to be replaced. For more info, please visit our website at
A different approach to serially connected modems has been jointly developed with Rockwell which allows for wireless control utilizling the SLC platform. This method uses direct backplane connectivity whereas the RF data is mapped into I/O image tables and scanned/updated by the SLC processor as with standard I/O modules. This eliminates typical latency that a serial device presents. Two places to find out more info are on Rockwell's Encompass Partner website under Radio Frequency Contol Modules
and at Control Chief also manufactures a Watchdog Relay module for connectivity to MLC circuits on the machine end of the control link. If the websites leave any unanswered questions, contact Technical Sales at (800)233-3016 ext 224.

Ben Brechtel
[email protected]
We manufacture a 2.4 GHz wireless modem that will work for this application.

Briefly the modems feature:

- Industrial Temperature -40C to +75C
- 6vdc to 28vdc input power
- Full Duplex, Asychronous data rates to 115.2kbps
- 32 channels with up to 254 radios per network channel
- Dual antennas for antenna diversity
- Each radio can be configured as either a master, a remote, or a store and forward repeater.
- UL1604 Class 1, Div 2 Groups A,B,C,D Hazardous Location rating
- RS-232 AND RS-485
- Integrated Modbus support
- Point to Point range of 15 miles. Extendable with repeaters.
- Over the air configuration
- Easy to use, Windows based configuration and diagnostic software with integrated RSSI and Signal to Noise Ratio meters
- Wireless Ethernet Version due October 2001.

You can find more information at