# A question about a sensor in a metallic enclosure

I need to mount this sensor inside an aluminum or metallic enclosure. Then the sensor will stay inside the enclosure. The enclosure will be mounted outdoors on a bridge concrete or some part I dont know.

In above figures, blue is the cable for sensor wires, gray is the enclosure. Enclosure has IP67 rating so waterproof ect.

The sensor's metallic case is not connected to sensor ground. But when I inject earth noise to the case it somehow capacitively couples as noise.

I have too option: either I will directly mount the sensor's metallic case to the enclosure or I will mount it on a wooden or plastic plate and isolate the direct contact with enclosure.

Is it better to mount the sensor as in Figure 2?

• what is earth noise? – jsotola Jun 2 '18 at 19:35
• I mean when I connect the AC mains earth to the metallic case of the sensor(accelerometer) by alligator clips; I can see noise coupling even though the metallic case of the sensor is not connected to sensor ground. – HelpMee Jun 2 '18 at 19:38
• From what I see in the documentation, those sensors are already environmentally sealed and come with optional sealed connectors. Those things already their own enclosures of high quality.You can't get any better than that, I think. – Maple Jun 2 '18 at 19:41
• disconnect the device from the cable inside the enclosure and run the test again .... your cable may be acting as an antenna – jsotola Jun 2 '18 at 19:42
• 1) how do you measure the noise? 2) Where do you measure the noise? 3) Can you measure the same noise if the wires are disconnected from the sensor and shorted together? 4) can you measure the same level of noise from the outer case? Many things you can try and many things you have not said. – Andy aka Jun 2 '18 at 21:08