Carrying an analog signal from one kilometer


Tanweer Ahmed

Dear Imran,
You can do it two ways.

1. You can take the signal via a modem or any other comm link preferred for your system.

2. Convert your analog signal probably 4~20 mA to 10~50 mA and convert back to 4~20mA at the controller location, such a signal conditioners are common, easily available and inexpensive. I hope a 10~50mA signal can easily be transmitted through 1km distance.

Tanweer Ahmed
[email protected]
if you have wire between the sites use inexpensive AI to pulse and Pulse to AI, signal conditioners, Action Instruments makes a couple of good units. We have used before on Municipal projects

Al Pawlowski, PE

If you don't already have a cable installed between the two points (for 4/20mA or a simple modulation technique like pulse tone), you might look into a new un-licensed radio telemetry product from Devar ( that they call their model PS1 and PS2. I don't have any experience with it; it's new. There are others, of course, but this one is about as low an over-all cost as I have seen.
Considering that the ISA S50 standard for 4-20 mA transmission specifies that you should be able to take a 24 VDC 4-20 mADC (isolated, into 1000
ohms) up to 5000 feet (which is about a kilometer and a third), you must be looking for some way to do it without stringing a kilometer of wire.

There are several companies who make spread spectrum (900 mHz) RF transmitters for converting an analog signal, and carrying it short distances. I can't off the top of my head think of a name, though. Anybody else?

Walt Boyes

new job: Director of New Business Development
Branom Instrument Co.
Seattle, WA

Walt Boyes -- MarketingPractice Consultants
[email protected]
21118 SE 278th Place - Maple Valley, WA 98038
253-709-5046 cell 425-432-8262 home office
The other day I posted that I knew of a couple of companies that provided wireless analog transmission, but couldn't remember their names. I looked one up: Isaacs & Associates of Walla Walla WA. Their website is

Walt Boyes
Current loops travel well. As long as the wire resistence does not cause the voltage limits to be execeeded, they will travel as far as you want with no hassle.

Kiel-1, Larry

I just saw a transmitter that will do the conversion for up to one mile. I saw it at a conference so I don't really know how well it works. The company is Adcon Telemetry and they can be reached at or 800-360-5309. The product was called a 4-20ma Radio Link.

Larry Kiel
I tested a very robust unit from RFData Corp about a year ago. It was a frequency hopper with integrated analog and digital i/o packaged in small DIN rail enclosures . You might try their web site at for more details , but I recall they had various configurations and numbers of channels for analog in and out .

Marius Tudor

Elmar Tech

Robert Phillips

What about the problem of lightning damage when buried? We have repeated failures we suspect that are due to lightning and are looking at radio solution.
Robert Phillips
Cypress Water Purification
City of Wichita Falls, Tx

At 11:34 PM 3/3/00 +0100, you wrote:
>Current loops travel well. As long as the wire resistence does not cause the voltage limits to be execeeded, they will travel as far as you want with no hassle.<

Brian Rode Engineered Handling Inc.

If you can run wire there is a great product from Sensor Pulse that is around $180.00 US that converts Analog to a digital serial communication. It comes with drivers for most PLCs Check it out it works great

Phillip Costantinou

How about a Weed Instrument 4-20 mA to fiber-optic transmitter/receiver?
800 880 9333
Round Rock, Texas, USA
Digimux allows you to multiplex upto 4 analog signals on one cable, the FOTR series lets you do single channels, and the FOR-CC/FOT-CC does single contact closures distances from two miles on up (depending on type), total electric isolation, lightning immune, EMI/RFI free, no ground loops/potential problems, low maintenance
approximate costs (all USdollars):
transmitter: $785
receiver: $785
cable: $0.80 / foot

Phillip Costantinou, P.E.
I C Thomasson Associates
Nashville, TN-USA