上圖為機械式壓力開關，工作原理是兩個空間氣壓變化時，膜片上的兩個金屬觸點開或合，達到導通電路的作用，體積大，精度差，成本低。我們用壓力校驗儀進行了測試，發現壓差到100帕時，設備仍未動作。有些施工單位為減少成本而選用機械式壓力開關來代替余壓探測器，萬一發生火災，無法聯動泄壓閥，防火門無法正常開啟會造成嚴重后果。
2.免接氣管式余壓探測器
免接氣管式余壓探測器采用絕壓式壓力傳感器芯片，直接測量前室或樓梯間大氣壓的變化。此方案不符合標準規范，并且很難測量準確。標準要求是：1.前室、封閉避難層(間)與走道之間的壓差應為25Pa-30Pa；2.樓梯間與走道之間的壓差應為40Pa～50Pa。標準明確要求了余壓值是前室/樓梯間與走道的一個壓力差值，并不是加壓區域的大氣壓值的變化量。并且標準大氣壓是在10萬帕以上，測量設備很難達到幾帕的誤差，25-30Pa，40-50Pa這個區間控制不準確。
六.問題解決辦法
1.在設計階段，圖紙應該明確要求采用數字式余壓探測器，能夠直接通過屏幕觀察到余壓值，并且25-30Pa（前室），40-50Pa（樓梯間）應設置成定值，不允許改動。
2.系統驗收時，用手持壓力校驗儀（推薦型號希瑪AS510）對余壓系統進行加壓測試，當壓差值加到30Pa（前室探測器）或50Pa（樓梯間探測器）時，觀察探測器是否發信號動作，泄壓閥是否聯動。
3.系統驗收時，查看探測器氣管安裝是否規范，測量的是否是前室與走道，樓梯間與走道的壓差。
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