Remote Data Acquisition

Maybe some radio technique? There are short-range radio systems that can do this, but I don't know about your distance.

do you mean the line of sight?

in order to avoid such problem i search for GSM solution

This is what I have use:

http://www.multitech.com/en_US/products/families/socketmodemgprs/

Depending of what i have need I attached some more stuff.

1) Why GPRS?
If the only available network in your area is GSM, why are you inquiring about GPRS? You either have the service or you don't.

2) GPRS or GSM?
The white paper here:

http://rd.phoenixcon.com/wireless/GPRSwhitepaper.pdf

describes why continuous monitoring is best done with GPRS (written for the USA market, but I can't imagine the cellular billing is that different in other parts of the world), as opposed to GSM.

GSM works well for report-on-exception or periodic 4x/day reporting, but is not designed for continuous monitoring for those who have budgets that are not unlimited.

3) analog to what and how?

What do you expect to see at the central control panel?

If you could even get a GSM text message, how would it be displayed on a control panel in the absence of SCADA or an internet server?

If you managed to convert 4-20mA to a digital signal (RS-232) what protocol would be used to manage the connection, fetch the data and do something with it, in the absence of SCADA or an internet server?

4) Does the remote site have internet access?
Does the control room have internet access?

1- sorry for inconvenience, but when i mentioned the GSM network i mean the physical connection but the GPRS service is available in the network.

2-thank you for the paper, really i had never known the different between them perviously.

3-i need the analog signal (this will be through PLC connected to the serial port of the modem or GPRS controllor) or digital outputs from GPRS controllor at different setpoints

4- neiher the remote site nor the control room has internet access

The only information provided is:

> pressure TX (4-20mA signal)

> 3-i need the analog signal (this will be through PLC connected to the serial port of the modem or GPRS controllor) or digital outputs from GPRS controllor at different setpoints

>monitor it by the central control panel

So I'm not clear on what is being attempted:

I can figure out that the pressure transmitter is connected to the PLC. The PLC has a serial port.

a) Is the PLC doing control based upon the pressure input?

b) Is the task to send setpoints from the control room to the PLC, as well as "monitor it by the central control panel"?

c) Is what you call a 'GPRS controller' different than the PLC?

d) If yes, where is the GPRS controller? control room or field?

The key here is that you're focusing on wireless when what you need is a control strategy. Wireless just replaces wire. One does not depend on 'wireless' to do control or to monitor or to do tasks that are in the domain of controllers (PLC's) or HMI's. Wireless just carries the signals between a controller and an HMI, like wire does.

You first must have a control system that would work over wire - some form of HMI that can send setpoints to the PLC and display pressure readings from the transmitter/PLC. That includes a digital communications protocol which the controller and the HMI use to 'talk' to one another.

Then, and only then, do you look for wireless components that will replace the wires between the HMI and the PLC.

let me clarify some points:

1- i have 2 sites (one is 25km far away from the other site)

2- the first site: has only pressure TX, this signal should be transmitted to the other site.

3- the second site: has control panel and actuated valve, where according to the received pressure signal the actuated valve will be opened or closed automatically.

4- when i am looking for GPRS controllor, first to be installed at the two sites (one send and the other receive). second substituting for installing GPRS modem and PLC

5- i hope every thing will be cleared now.