As Minewatch PS21 but including 6 intrinsically safe to flameproof interposing relays for the control of mining flameproof switchgear.
The main transformer and relays (Minewatch PC21-R) are housed inside a cast steel flameproof enclosure with 6 FLP entries for supply and control cables. The Minewatch PS21-B also includes a sheet steel intrinsically safe battery enclosure. All variants have a sheet steel intrinsically safe terminal chamber for connecting the 12V dc to intrinsically safe controllers and/or sensors; alternatively, the Minewatch PS21 can be directly mounted to a Minewatch PC21 intrinsically safe controller to provide a composite unit.
The 12V dc output is regulated to maintain the output voltage to a minimum of 11.5V up to the full load capacity of 700mA. The Minewatch PS21-B will maintain this output at full load for an 8 hour period. The Minewatch PS21-B also contains an intrinsically safe opto output to indicate to the intrinsically safe controller when the power supply has changed from mains to battery.
In the case of the Minewatch PS21-R, up to 6 FLP control relays can be operated by an intrinsically safe controller (such as a Minewatch PC21) and interlock to FLP control circuits.