A B737-300 FLT CREW DECLARED AN EMER AND EXECUTED AN EMER DSCNT IN RESPONSE TO A CABIN ALT WARNING HORN. THE EXCESSIVE CABIN ALT WAS DUE TO A MISSET PRESSURIZATION PANEL.

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FLT TO ZZZ1 WAS THE 3RD LEG OF THE DAY; DAY 3 OF A 4 DAY TRIP. MY FO IS A NEW HIRE WITH LESS THAN 100 HRS. ALL PREVIOUS FLTS WERE UNEVENTFUL. PUSH WAS NORMAL WITH ALL PREFLT CHKLISTS ACCOMPLISHED. THE SPECIAL DEP WAS FULLY BRIEFED AND FLT WAS FLOWN AS CAPT'S LEG. THE CLB CHKLIST AT 10000 FT INDICATED NO ABNORMAL PRESSURIZATION PROBS. DEP AND INITIAL CLB WERE UNEVENTFUL. CLBING THROUGH FL300 FOR FL330 THE CABIN ALT WARNING HORN SOUNDED. I NOTED THAT THE CABIN ALT WAS AT 10000-11000 FT BUT NO PRESSURIZATION PANEL OR MASTER CAUTION LIGHTS WERE ILLUMINATED. CABIN ALT WAS CLBING AT APPROX 500 FPM. WE DONNED OUR OXYGEN MASKS; ESTABLISHED COMS; DECLARED AN EMER AND INITIATED AN EMER DSCNT ALMOST SIMULTANEOUSLY. I HAD THE FO COMPLETE THE CABIN ALT WARNING HORN/ABNORMAL PRESSURIZATION AND EMER DSCNT CHKLISTS WHILE I COORDINATED WITH CENTER. I THEN HAD THE FO TELL THE FLT ATTENDANTS THAT WE HAD A PRESSURIZATION PROB AND THAT WE WERE DSNDING TO A LOWER ALT. WE LEVELED AT 9000 FT MSL; REMOVED OUR OXYGEN MASKS AND REVIEWED THE QRH CHKLISTS. DURING THE DSCNT; THE CABIN ALT DID NOT GO ABOVE APPROX 11000 FT MSL SO THE PAX'S OXYGEN MASKS DID NOT DEPLOY AUTOMATICALLY; NOR DID WE DEPLOY THEM MANUALLY. THE FO THEN NOTICED THAT THE LAND ALT SET FOR THE ARR ARPT (ZZZ1); AND THE CABIN ALT WERE BOTH SET INCORRECTLY. THE ZZZ1 ARPT ELEVATION IS APPROX 1100 FT MSL AND THE LAND AND CABIN ALT HAD BEEN INADVERTENTLY SET TO 11130 FT MSL. I CONCLUDED THAT THE ABNORMAL PRESSURIZATION WAS A RESULT OF THE INCORRECT LAND AND CABIN ALTS. WE DIALED IN THE CORRECT LAND AND CABIN ALTS AND RETURNED TO THE AUTO MODE FROM MANUAL MODE AND THE CABIN BEGAN TO PRESSURIZE NORMALLY. WE REVIEWED OUR FUEL SITUATION AND DETERMINED THERE WAS SUFFICIENT FUEL TO SAFELY PROCEED TO OUR SCHEDULED DEST (ZZZ1). ENRTE TO ZZZ1 WE COORDINATED WITH ZZZ1 OPS AND MAINT REGARDING THE ABNORMAL PRESSURE EVENT. I ALSO BRIEFED THE FLT ATTENDANTS AND PAX THAT WE HAD EXPERIENCED AN ABNORMAL PRESSURIZATION AND THAT WE WOULD BE FLYING THE REMAINING PORTION OF THE FLT AT A LOWER ALT AND THAT WE HAD SUFFICIENT FUEL TO DO SO. THE REMAINDER OF THE FLT TO ZZZ1 WAS UNEVENTFUL. ALL DSCNT; LNDG AND PARKING CHKLISTS WERE COMPLETED NORMALLY. AFTER DEBRIEF WITH THE FLT ATTENDANTS; THEY INDICATED NO PAX SEEMED TO EXPERIENCE ANY DISCOMFORT DURING THE DSCNT OR REMAINING PORTION OF THE FLT. AT THE GATE I NOTIFIED DISPATCH AND THE CHIEF PLT.