Cảm biến tiệm cận là gì? Những vấn đề xung quanh cảm biến tiệm cận
Là một loại cảm biến quen thuộc có trong mỗi chiếc Smartphone, nhưng đến nay vẫn còn rất nhiều người chưa biết cảm biến tiệm cận là gì? Có những loại cảm biến tiệm cận nào? Nguyên lý hoạt động, cấu tạo và ứng dụng ra sao, nó có vai trò gì trong các thiết bị điện tử hiện đại,…? Chỉ cần bỏ ra 2 phút đọc bài viết sau, bạn sẽ hiểu rõ hơn về những vấn đề này!
- Đầu tiên cần phải biết:
Cảm biến tiệm cận là gì? Có mặt ở những thiết bị nào?
Cảm biến tiệm cận hay công tắc tiệm cận, sensor tiệm cận, PROX có tên tiếng Anh là Proximity Sensors là loại cảm biến có khả năng phản ứng khi có vật ở gần nó, thông thường là vài milimet (mm).
Cảm biến tiệm cận thường được lắp tại vị trí cuối của chi tiết máy, tín hiệu đầu ra của cảm biến này sẽ có chức năng khởi động một chức năng khác của máy.
Ưu điểm lớn của loại cảm biến này là nó có khả năng hoạt động tốt ngay cả trong môi trường khắc nghiệt nhất.
Có những loại cảm biến tiệm cận nào?
Có khá nhiều cảm biến tiệm cận công nghiệp. Nhưng chỉ có 2 loại chính có thể kể đến, đó là: Cảm biến tiệm cận điện cảm (hay còn gọi là cảm ứng từ) và cảm biến tiệm cận cảm ứng điện dụng. Trong đó:
>>> Cảm biến tiệm cận điện cảm – Proximity:
Phát hiện vật bằng cách tạo ra trường điện từ. Tuy nhiên, loại cảm biến này chỉ có thể phát hiện các vật bằng kim loại.
- Loại này lại tiếp tục được chia thành 02 loại, là:
+ Cảm ứng từ có bảo vệ (Shielded): Từ trường được tập trung ở trước mặt sensor tiệm cận nên có ưu điểm là:
ít bị nhiễu bởi kim loại xung quanh
Tuy nhiên, điều này lại khiến khoảng cách đo bị ngắn đi.
+ Cảm ứng từ không có bảo vệ (Un-Shielded): Vì không có sự bảo vệ từ trường quanh mặt sensor nên khoảng cách đo dài hơn loại cảm ứng có bảo vệ. Tuy nhiên nó lại:
dễ bị nhiễu bởi kim loại xung quanh.
>>> Cảm biến tiệm cận điện dụng
Còn gọi là capacitive sensor. Cảm biến này:
… phát hiện vật thể ở gần theo nguyên tắc tĩnh điện
Tức là dựa vào:
…sự thay đổi điện dung giữa vật được cảm biến và đầu sensor cảm biến
Loại này có ưu điểm lớn là có thể:
phát hiện tất cả vật thể.
Lưu ý:
Dù cảm biến tiệm cận điện cảm chỉ có khả năng phát hiện các vật bằng kim loại, nhưng chúng được sử dụng phổ biến hơn trong công nghiệp bởi các loại cảm biến này:
+ Ít bị nhiễu hơn
Và…
+ Rẻ hơn
Đa phần cảm biến tiệm cận điện cảm đều có đầu ra transistor có logic NPN hoặc PNP (còn được gọi là DC-3 dây). Trong đó cảm biến tiệm cận npn được sử dụng phổ biến hơn.
Cấu tạo của cảm biến tiệm cận là gì?
Về cấu tạo, các loại cảm biến tiệm cận gồm 4 phần:
Phần cảm biến, mạch dao động, bộ cảm nhận và bộ mạch tín hiệu đầu ra.
>> Nguyên lý hoạt động của cảm biến tiệm cận điện dụng, điện cảm là gì?
Cảm biến tiệm cận hoạt động theo nguyên lý trường điện từ (đối với loại Proximity Sensor), hoặc vùng điện dung (đối với loại capacitive sensor). Trường điện từ/ điện dung này phát ra quanh cảm biến trong khoảng cách tối đa đến 60 mm. Trong khoảng cách này, khi gặp vật thể nó sẽ phát ra tín hiệu và truyền về bộ xử lý. Tại đây, bộ xử lý sẽ chuyển đổi tín hiệu về sự chuyển động hoặc xuất hiện của một vật thể nào đó trở thành tín hiệu điện. Tín hiệu này có thể làm cảnh báo, hoặc dùng để điều khiển ứng dụng thông qua lập trình từ PLC/ máy chủ.
Để thực hiện công việc chuyển đổi này, cảm biến tiệm cận cần đến 3 hệ thống phát hiện tín hiệu, đó là:
Hệ thống sử dụng sự thay đổi điện dung khi đến gần vật thể cần được phát hiện:
-
-
-
- Hệ thống dùng nam châm
- Hệ thống chuyển mạch cộng tử
-
-
Đặc điểm của các loại cảm biến tiệm cận là gì?
Các loại cảm biến tiệm cận có những đặc điểm sau:
- → Khả năng phát hiện vật thể không cần tiếp xúc trực tiếp, không tác động lên vật. Khoảng cách phát hiện xa nhất có thể lên đến 30 mm.
- → Khả năng hoạt động ổn định, chống rung, chống sốc tốt
- → Tốc độ đáp ứng cực nhanh, tuổi thọ cao hơn nhiều so với công tắc giới hạn thông thường (limit switch)
- → Đầu sensor cảm biến cực nhỏ – lắp được ở nhiều vị trí khác nhau
- → Có thể hoạt động tốt trong điều kiện môi trường khắc nghiệt
Ứng dụng của cảm biến tiệm cận là gì?
Cảm biến tiệm cận rất phổ biến trong các ngành công nghiệp, nhất là công nghiệp nhà máy, điện tử. Chúng có thể được gắn trên các dây truyền sản xuất, điện thoại thông minh, xe ô tô…
Mục đích sử dụng cảm biến tiệm cận phổ biến nhất thường là:
- Kiểm soát chất lỏng trong bể chưa, hộp giấy
- Kiểm soát kim loại
- Kiểm soát số lượng.
Những lưu ý khi sử dụng các loại cảm biến tiệm cận
Dù mang lại nhiều lợi ích trong các ngành công nghiệp hiện đại. Song, khi sử dụng cảm biến tiệm cận người dùng cần phải xác định mình đâng đo cái gì? cần tốc độ xử lý cảm biến nhanh hay chậm, cần độ chính xác cao hay không? Bên cạnh đó, cần:
+ Kiểm tra kỹ sức ảnh hưởng của môi trường xung quanh khu vực đo xem có từ trường lớn hay không (ví dụ: Nam châm), vì đây là một trong những nguyên do dẫn đến sai số khi đo của cảm biến.
+ Khu vực đo rung hay không, nhiệt độ môi trường cao không, khoảng cách từ cảm biến đến vật cần đo là bao nhiêu?
Tóm lại, tuy vào nhu cầu cũng như mục đích sử dụng của các nhà máy khác nhau mà bạn nên kiểm tra thật kỹ và chọn mua các loại cảm biến tiệm cận thích hợp để có thể đáp ứng tối đa nhu cầu cần đo.
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