The ELD-1 can be powered from two sources, directly from the network or by its internal lithium pack which operates the unit for up to two years.
Pressure Measurement The solid state pressure sensor measures the pressure in the hose wall over a 0-20 bar range to a resolution of 0.4% of full scale. There is accommodation for a second ambient pressure sensor as an option.
Data Storage The ELD-1 measures pressure every 10 minutes and stores the current pressure and the maximum pressure since the last query. The following data are transmitted: sensor ID, hose pressure, ambient pressure, max ambient pressure.
Electronic Network Up to 256 units can be connected in parallel onto the same 2-wire current loop. The network operation commences when power is applied to the current loop. Each sensor immediately samples the pressure, waits for a number of seconds equal to its ID number, then transmits its data as current pulses at 256 baud.
Optical Readout An optical interface is provided as a backup if the network fails or so ELD units can replace the old style visual indicators in a hose system without imbedded wires. Thus divers can be used as an emergency backup.
|The Hand Held Unit (HHU)|
The HHU is used to read out information from the ELD-1 or a network of ELDs. The HHU is turned on and held above the ELD so it shines into the polycarbonate dome. The HHU and ELD communicate at 256 baud by serial modulation of visible light emitting diodes shining into silicon cell receivers. Visible light is attenuated in water much less than infrared and thus is much more reliable for an optical link in water.
The ELD and HHU communicate in an error free and redundant packet protocol. The HHU checks each data transmission and repeats the query until is received error free.
Once the data has been transferred into the HHU successfully, the ELD memory is reset and a green indicator light flashes. The operator can turn off the HHU power and proceed to the next ELD or back to the base station to download the stored data. Each ELD data set is stored with local time and the unit ID number. There are no errors and no numbers to write down during the dive.
Hundreds of data packets can be stored in the HHU. At the base station the HHU can be read into a computer by either (a) direct RS232 serial data transfer or (b) IsDA optical readout.