Automation system question.

I'm unsure what level of technology you are asking for. I'll assume you wish to buy a commercial system. Select a programmable multichannel multiplexed analog to digital (if your signal is indeed analog) capture card or box. You can choose which channel is sampled at what time allowing you to select certain channels at lower rates and certain channels at higher rates. This provides a great deal of flexibilty in customizing the solution for your specific needs while only capturing the amount of data necessary to reconstruct the original signal in digital form. National Instruments is an excellent place to start looking for data capture boards.

Are you only measuring or do you need to further process the signals? You say it is an automation system, so I am going to assume that you need to process the data that you capture. You can use a PLC for capturing the data - most PLCs now have analog and digital input capabilities. The PLC programming interface will allow you to take your signals and perform many specific functions on them. If the size of your PLC program is not too large, datalogging every 10ms is easily doable. You can use timer functions in the PLC programming interface to retrieve the longer-interval data. Choosing the best solution depends on how accurate your data must be and how many signals you need to process.

By the way, how many analog signals do you need to process? How many digital signals do you need to monitor? How many digital control lines will you need? How many analog control outputs will you need?

Answer these questions and I can steer you toward some specific solutions.

Mike

First of all, thank you all very much for your help so quickly. The system is not yet defined, i may use a industrial pc or a pac instead of the plc.The system has 2 layers of control, this one is the most close to the sensors and performs 70% of the control, being much of that control dedicated to the generation of alarms to the upper control layer. I have aproximatly 40 analog inputs and 10 digital inputs, the output is about 3-5 analog signals and the rest is to be sent to ethernet.

Question: do you want to measure a value (voltage, current,resistance) periodically (say every 10 mS) or do you want to detect that an event has occurred by testing for that event every 10 mS (or 120 mS or 5 minutes etc)?

The cheapest way to do this would probably be a desktop computer with input and output cards chosen to fit the number of analog inputs, the number of digital inputs and the number and type of outputs planned. As was already said, National Instruments have a wide choice of cards and a very flexible and relatively easy to program software.

Generally, after a system is implemented there is still a lot of tweaking to be done. These changes are much more easily done on a computer based system compared to a PLC based system.

Tu estas buscando un disparador y no estas dando los parámetros de funcionamiento, o su uso, como un medio a ser medido; luz, calor, temperatura, presión, etc., lo quieres en funcionamiento continuo o pre-fijado a una lectura, la respuesta a un evento puede ser en continuo (lineal) o con un retrazo (o temporizado).

10 mili segundo en electrónica es lento, puedes tener de respuesta simultánea (pico segundo), o lo que demore la carga de un condensador (circuito RLC), tan barato como un dólar o tan caro según lo que quieras controlar.

10 minutos: que se demore entre que recibe la señal y termine su función, o a los 10 minutos se dispare la señal de respuesta.

"DA UN EJEMPLO DE LO QUE QUIRES"

English translation of your message is requested.

A helpful resource:

http://ets.freetranslation.com/

Encuentro muy interesante el hecho que Usted responda en Español. Obviamente Ud. lee Inglés, o no sabría de que se trata. Sospecho que no somos muchos en este sitio que entienden Español. Por supuesto hay algunas personas que no entiendan si el Inglés no es perfecto, pero esas personas no son las importantes. Sugiero que Ud. trata de responder en Inglés, o tal vez en las dos idiomas.

Dick

I am outside practice with my English:

Your these looking for a trigger and these not giving the parameters of operation, or their use, like means to be measured; light, heat, temperature, pressure, etc., you want it in continuous operation or pre-fixed to a reading, the answer to an event can be in continuous (linear) or with delay (or time-lag). 10 mili second in electronics is slow, you can have of simultaneous answer (very quickly), or what delays the load of a condenser (circuit RLC), as cheap as a one dollar or expensive according to which you want to control. 10 minutes: that it is delayed while it receives the signal and it finishes his function, or to the 10 minutes the answer signal goes off.

"GIVES AN EXAMPLE OF WHICH"

Tomás

Hi Thomas,

English is a very hard language to learn as a first language let alone as a second. You might be out of practice, but I can assure you that your written English is perfectly understandable. It's actually considerably better than some of the idiots that I am forced to deal with that use English as a first language.

Keep up the good work.

Regards MASU

Gracias Dick

Tomás

First of all you need to understand how PLCs work. In general they are not interrupt driven. This means they DO NOT react to the change in status of a single input. Here is a rough flow chart of how they work.

1. Read data from input ports and store values in memory.
2. Set program counter to 1
3. Execute User program according to program counter and input data stored in memory.
4. Write results of interpretation to memory
5. Increment program counter
6. Go to step 3 if program counter not at end of user program
7. Write date stored in memory to output ports
8. Go to step 1

This all takes time and depending on the PLC may take more than 10 ms. As a result you may miss a change in the data if it is varying more often than the time it takes the PLC to carry out a full cycle.

Something else that you may not be aware of is that because the users application is executed sequentially changes in the status of an output of internal register are only available to lines in the program that are after the change. For example, if and output that is set by line 1 of you program, is dependent of the status of an internal register or point that is set in line 2, the updated status that is generated by line 2, will not be available for use by line 1 till the next scan cycle of the PLC.

Some PLC manufacturers however make high speed input devices for use in situations where the date is changing more rapidly than the PLCs scan rate. They work by storing the values and then transferring a block of values when the port is scanned.

All up I can't see the need to have a separate PLC for each, provided you either have a system that is capable of scanning and updating the port status in less than 10 ms, or alternatively, has a high speed input option that can be used to monitor the 10 ms device.

A plc may not be what you need. A DDC may fit better. Innotech Control has several small and large controlers, which will do the features you discribed. Check out www.innotech.com.au the software is free from the net, it includes simulators and such so you can test the product with out spending a dime. then if you like it all you need is the controller.

In the industrial environment I find any control system that relies on a Personal computer does not have the up time or stability to be reliable.

Programmable controlers (PLC's) are designed to run 24/7 without crashing, virus problems or having some user sit down and play a game and tank the whole system.

The old Reliance Automax system was very capable of running as fast as 2 msec control loops, and that technology is almost 20 years old. The AB Control Logix system is more than capable of running both fast and slow sampling symultaneously, setting alarms, interfacing via ethernet to SCADA systems, and closing control loops both fast and slow. I am sure any of the new high end PLC's from most major manufacturers have similar capabilities.

I would only use a PC if it is monitoring in a non-critical environment. It is only a matter of time before hard drives crash or Windows gets in the way. If a re-boot is not tolerated, don't use a PC.

Just my 2 cents worth.

You definitely do not need separate PLCs. Depending on the application behind the measuring the variables, 10ms is not to hard to achieve. Also, you can program in interrupts that force an I/O scan regardless of the program scan time. The size of the system you describe is pretty small so there should not be a problem in achieving your goals although the goals are a little vague right now. Can you at least give us the basic process description at this point?

Liked your last bird line.

Reminds me when I was a youth, racing my brother down a hill on our bicycles.

Suddenly he flies of his bike and goes tumbling down the ditch! What ????

He gets up and dusts himself off, and there is a gigantic bird poop across his eye and down his face.

Could have been an Americas Funniest Video, (but like so many of those, they don't show how banged up the victim was).

Very interesting !

But since this is a technical forum, I would like to know what speed exactly he was coming down the hill. Did he turn on his dynamo ? If so how many volts was it producing ? How many revolutions per second were necessary to obtain this voltage? What kind (brand and serialnr. please) of grease was used to grease the chain of his bike ?

Also interesting to know would be wich eye the bird poop was? And from what kind of bird was it ? Was it a domestic bird ? Also what was the exact weight of the poop ?

YOu also say that the bird poop ran down his face. We like to know at what speed, and what direction. This might be an indication where the bird was coming from, and at what speed it was flying.

Please provide answers ASAP. This utmost interesting technical stuff !
Thanks for sharing !

8% grade

CCM bicycle, coaster brakes.

About 100lbs for cyclist

Approx 20 mph

White poop, approx 10 cc

Shell 10w30 motor oil

No electrical generating equipment on board

Time of flight approx .5 seconds

High speed input cards are available for a variety of PLCs. Check out Allen Bradley and Siemens (usual disclaimer) as a first step.

During a controls systems training course back in the 1970s the lecturer stated, "Slug everything with a 1-second time constant. On most plants, if it happens in less than 1 second then it isn't real."

What does this conceptual system control and why are milliseconds important? Weapons systems? Aircraft auto-land?

The process is a wind turbine, so the power needs to be constantly monitored to check the quality of the power to be delivered to the network. The electrical variables (power,current,voltage...) are the ones that need to be measured in the ms intervals, and the mechanical variables (vibration,tilt...). This is a system composed of 5 wind turbine, each with a controler and a main wind farm controler that receives the required power to be delivered and adjust the turbine for that objective. So the controler to develops will measure all the data from the sensors of the turbine and check with the formulas to see if everything is OK, if not, it sends an alarm to the wind farm controler, that is conected to the scada. Hope this describes the system :) The main question i had was already answered, i have no need for 2 plc´s but now i had a deeper knowledge of the option i have now with your answers, thank you.

For the PLC to perform the control then the data acquisition and scan speed required is based upon how fast can variables change and how fast will they react to control signals. To be a little more specific, the processor logic scan time must be at least two times faster than the time the process will respond to a control output thereby creating a feedback response (loop deadtime). From what I can tell by the description provided, the acquisition speed of standard analog and digitial input cards should be adequate for this application. If you want to measure very high speed digital inputs or frequency signals directly then you will need to select a frequency input card for the PLC to "see" those signals.

Good luck! It sounds like a fun project and I wish I could participate more.

Hello, we manufacture a system that can transmit 4-20ma data wirelessly. We also manufacture a system that allows you to monitor 4-20ma and digital data via the internet. Take a look at our website: www.remotecontroltech.com.

Thank you,

Sara