Automatic dialup to remote stations

Scream has the ability for a central acquisition system to poll remote stations connected to modems, collecting any data that has been stored. This feature is intended for use in conjunction with the flash recording modes of digitiser modules (eg. Adaptive, FIFO, dual), and triggering configurations.
Multiple modems, and multiple telephone numbers per modem are supported.

Hardware arrangement

When Scream opens a serial port, it checks for the presence of a modem. If found, it enables the dialup configuration option for that serial port. Each port (and therefore modem) connection can have a separate configuration.

In this manner, a bank of modems can be assembled allowing simultaneous polling of remote stations.

Alternatively, station connections can be separated into different phone lines depending on call costs for providers. For example, you can call stations connected by land lines on a normal phone line modem connected to one serial port, but stations connected by cellular phone from a cellular modem, connected to a different serial port.

As polled modem operation is not conducive to real-time continuous data acquisition, it is expected that the digitiser will be configured for either:

• triggered mode, where event data is stored in Flash memory until next poll, or
• low sample rate continuous mode, where the data rate is significantly lower than the modem connect rate. For example, if the modem connection can achieve 19200 baud, then a 200sps, 3 component station would require a continuous connection to collect all data. If the data rate was 1/10^th of this, e.g. 20sps, then a modem would expect to be connected 1/10^th of the time (e.g. if connecting every hour, or 60 minutes, then it would be online for 6 minutes collecting data).

Software arrangement

Each serial port (or modem) has it’s own configuration and polling schedule. The "Dialup Settings" window allows point-and-click setup of the options and phone list.

Each connected modem can have a list of telephone numbers to poll through. Commencement of the polling can be controlled either by a simple “Every n hours” rule, or by a more complex and controllable “Specified Times” rule. In this rule, multiple times of day can be entered, and which days this applies to.

When a time specified by the scheduling is reached, scream will connect in turn to each of the telephone numbers in the list, disconnecting from a station when all data has been received (the line goes idle).

To prevent one station from using all telephone time, there is an option to limit the duration of each call. If data reception has not naturally terminated by this time, Scream will disconnect the modem, leaving any remaining data for collection next time.

Under some circumstances, special commands are required for correct modem operation. These can be entered in the “Additional Modem Settings” box. These settings should consist of AT commands, but not include the “AT” prefix (Scream adds this automatically).

Finally, an overall “Active” option is available. This allows the dialup feature to be enabled and disabled without loss of all other settings.