Remotely Accessing
Telog Recorders

TEXT BEING WRITTEN OVER TIME

There are times when remote accessing of a Telog recorder ('Telogers' or 'Linecorders') is either vital or prudent in time saving. 3 methods are available being remote RS232 devices (LAN based), PSTN (standard telephone line), and/or Radio (either radio modems or cellular technology). Remote access of Telog Linecorders, R-2000, and R-3000 series data loggers can be accomplished with these techniques.

When doing stubborn complaints the best option is to have the recorder set to the shortest recording interval and then analyse the data on a daily basis. However, this will result in a costly high number of visits to site. Having a fairly standard optically isolated RS232 port, these recorders almost beg connection to a modem whether a standard telephone, cellular, or radio type. The optical isolation creates a few challanges but these are usually of no concern with most modems.

We discuss all these methods below together with their advantages and disadvantages. We'll start with the most common and move through to the most uncommon.

The Required Signals:

There are only 4 pins on the Telog unit that need to be connected, these are shown below together with the pin numbers. The pin configuration is the "9-pin equivalent of the standard 25-pin".

On a hardware front, the modem should be RS232 compliant i.e. capable of delivering a minimum of ±8V into a standard load (4k7). This is required to power the optically isolated port. The modem to also have a working DCD pin (indicating successful connection).

Note: During all of the set-ups listed below, the speed of communications between the Linecorder and modem is set to 9600 Baud. Older documentation of Telog's will show modem speeds lower than this. Effectively, this is a waste of on-line time especially in the light of the fact that modern modem technology is more than capable of this. When communicating locally with a Linecorder, ensure the data rate is 9600 Baud else the recorder will not work with the modem when installed in the field.

Programming and Testing the modem:

There are many "cheap and nasty" modems on the market and you would do well to steer clear of them. The modems featured here have been tested and proven. Should you not have these available, then a set of tests should be carried out on the modem to ensure it will work.

There are effectively only two operational requirements with regards the modem. The first is the modem should be completely "silent" when not on-line to another modem, the second is that the DCD pin be programmed to show when a connection is extablished.

The following are typical commands required to place the modem in a state suitable for working with the Telog units. Parameters shown in parenthesis (xx) are what has been found to be common amongst a number of modems.

PSTN (standard telephone line)

Public Switched Telephone Networks (i.e. standard telephone lines) are probably the most common method of accessing a remote location. Most sites have telephone lines available to both the user and recorder. The advantages are almost immediate access (if the line is installed) as well as a fairly reliable yet relatively inexpensive connection.

PSTN lines are not suitable for situations where none exist as the installation costs are usually prohibitively expensive. In such situations, refer to the section on Radio.

The diagram below shows the inter-connections between a Modem and a Telog Recorder ('Telogers' or 'Linecorders').

Personally, the only recommended range of modems is "MultiTech". Below is the set-up instructions for model MT5600ZD when used with a Telog recorder. Programming is done by connecting the modem to a PC and using any reasonable terminal program to send the commands to the modem. Note: The "enter" key must be pressed after entering each line as shown below.

Radio

Radio comes in two 'flavours', either direct radio modem links or dial up versions being cellular phone technology. The advantage of the latter is the ability for 'analogue' modems (standard telephone types) to access the cell networks if technologies such as GSM are used.

GSM

The Siemens M20T and MC35i have proven a most reliable form of "dial-up radio modems".

A suggested layout is shown alongside with the M20T built into a rugged box with an IEC320 mains connector on one side, and a 9 pin D type connector on the other (mimicking the socket on the modem itself). This facilitates the modem being kept some distance from the recorder which could otherwise be affected with strong 900MHz signals.

Below is the diagram to interconnect a Telog recorder to the Siemens M20T and MC35i.

Siemens M20T

Programming the M20T is relatively simple, but care must be exercised when issuing commands to the M20T. These are listed in the table below. Please note that the recorder is not asked to do anything strange with the M20T other than to dial. The reason for this is the baud rate modifies when issued with an AT&F command to 19200 baud. Also, it complicates testing if the SIM PIN or PUK is invoked. It will be noticed these are disabled in the M20T.

There are only a few things to be careful of. Once having obtained the SIM and accompanying number, you must also obtain a "data number" (this is a number the PC modem must dial to have the analogue modem signals converted into GSM data). The best method found is a "pay-as-you-go" number with data number (yes, there are such SIMs available) so that should the SIM be stolen, it is effectively useless after a few phone calls. Other contracts available are "receive only" or "limited calls" again to protect the SIM from running up an account.

Siemens MC35i

Programming the MC35i is even more simple than its older brother. Also, it complicates testing if the SIM PIN or PUK is invoked. These must be disabled before placing the SIM card in the MC35i.

If there are any questions please ask.