Pulse output from Utility Meters and Temp transmitter w/Micrologix

Hello everyone,

A customer wants to integrate their main electric (Qty 3) and gas utility meter (Qty 1) readings into a micrologix 1100. Each one of these 4 mechanical meters are setup to send out a pulse. however, each of these meters are about 5000 ft away from each other or the micrologix. Any ideas on how I should approach this issue and what it would take from hardware and programming perspective? I have some ideas but I would like to get some recommendations or the most cost effective way of doing it.

I also have a temperature transmitter that I want to connect to a micrologix 1100 that is at least 10000 ft away. The transmitter outputs a 4-20 mA current signal. Will I be able to run this signal that far, and if not, any ideas on how I would handle this?

Any advice is greatly appreciated.

Thanks,

Brij

5,000' is almost 1 mile; 10,000' is about 2 miles. That's a long distance to run cables.

Choices are copper, fiber, or wireless to get signals back.
Both copper and fiber face the issue of cable protection - trenching or poles? Costly.

I suspect that the ease of installing wireless will win the cost issue. Wireless can work if you work at locating the radio antennas up high enough to get 'reasonable' line of sight.

The 4-20mA temperature signal can be done with Phoenix Contact 1 way radio, no FCC license required. Simple to wire, what you put in is what you get out. 4-20mA in. 4-20mA out.

I would not recommend the antenna-on-a-beer-can style because the unity gain antenna is marginal at these distances.


I'd recommend the DIN rail mount radio

with the appropriate adapter cable to a yagi antenna


at the transmitter end, and a 5 or 6 dB gain omni on the receiver end. Use low loss cable to connect the radio adapter to the antenna (900Mhz radios eat up signal in non-low loss cable). All this stuff is available from Phoenix Contact.

That same radio can handle 2 separate input pulses if
- it is a dry contact that generates the pulse
- the pulse rate does not exceed the throughput rate of the radio

Like the 4-20mA, what you put in is what you get out: dry contact in, dry contact out

Even though the throughput is nominally about 20mS, one has to allow for missed or garbled transmissions, so I always double and double again the nominal value to 80mS. 80mS is equivalent to about 12Hz or 12 state changes per second. Most relays/dry contacts will chatter themselves to death at that rate.

I've configured flow meter totalizer outputs to change state on larger totals, say, every 1,000 gallons rather than every 100 gallons to minimize the state changes on the totalizer output.

Check out www.phoenixcon.com/wireless

It might be cheaper to have multiple PLC's and one wireless master. Then running all that wire and conduit. (4 ML1000, one ML1100) Run the nummbers (cost).

Does your customer own and control the meters, or does the utility? Having once worked for a utility, I know that they are very concerned when a customer connects ANYTHING to a meter.

If the utility owns the meters, it might be easier to install another set of company-controlled meters at a convenient point. Anyone can buy a meter and install it downstream of the service point for their own use, but not just anyone is allowed to monkey with the utility meters.

After we took a closer look at the facility and the meters, it is not really 5000 and 10000 ft away like the customer had initially mentioned to us. They were way off on the distances. They are only about 1000 ft away from each other.

I really like the idea of using multiple PLCs, that was my thought process as well but instead of a wireless master, I was going to run it back to the Master PLC via fiber, since they already have a ethernet to fiber convertors in the existing network.

The gas and the electric company has agreed to send a pulse and they are also providing a multiplier factor so now the customer is trying to integrate this data into their existing energy monitoring system.

Will I be able hook the pulse output from these mechanical meters to the PLC inputs or would I need like pulse input modules?

Also how far will I be able to run the 2 wire conductor with 4-20 mA current signal from the temperature transmitter.

I havent worked with analog signals before, After the physical connections, can anyone give me basic steps on how to get the readings from device. How do you calibrate and what are the typical programming instructions that you use to obtain the readings.

Thanks again for all the help.

Brij

That scope changed, huh?

Loop powered, 4-20ma routinely runs 5,000 ft. in large, spread out facilities like a refinery, on shielded, twisted pair copper wire with a 24Vdc power supply. 1,000 feet is well within capability, Dan

One note, if you haven't used analogs before: Isolation.

Most PLC brands have a choice of analog cards. The inexpensive analog cards typically have non-isolated inputs. The more expensive analog cards have isolated inputs.

Same thing with temperature transmitters. The less expensive transmitters are non-isolated, to get isolation costs more.

Isolation comes into play because a ground loops and common mode voltage in the circuit.

There are isolator modules (4-20mAin / 4-20mA out), usually put in the PLC panel, to eliminate ground loops and excessive common mode.

I find it pays to buy isolated transmitters and isolated inputs. But to each their own. Some times you can get by with a non-isolated device and it's only the combined effect of multiple analog inputs that cause a problem.

Dan

Find out the brand and model of the meters, then download the manual for each meter from the manufacturer's web site. Only then will you know the exact pulse output and what you will need to measure it.

A pulse output from a meter is by definition an electrical signal. The meters may be the mechanical type, but to produce a pulse, they will have a pulse-generation module. The utility company will take care of this for you. Many electric meters now have a built-in pulse for remote monitoring. It is simply a voltage that goes on for a short time, then back off. It is set to occur every X units. To monitor a meter pulse with a PLC requires nothing more than an Isolated PLC Input module that will accept the voltage range of the pulse (typically 120 volts AC), and an internal counter in the PLC. (If you are lucky, the meter might even have a dry relay contact that goes on during the pulse output, in which case you will not need Isolated Inputs.) After that, you must do some scaling to convert the pulses into units of KWH or Cubic Feet for the gas meter. For example, if 1 pulse = 0.1 watt, then you would multiply your Counter Accumulated value by 0.1 to get Watts, and by 0.0001 to get Kilowatts. To convert to Kilowatt-Hours, you have to also use a PLC Timer to record each measurement period. For example, set a timer for 1 hour, count pulses for one hour, then scale the pulses to get Kilowatt-Hours (Kilowatts per hour).

Generally, 4-20 milliampere signals can be run for 5000 feet, but it really depends on the output power (watts) of the signal transmitter, and the size of the wire used.