Cables Can Carry Vibrations to Isolated Systems
Vibrations introduced into an isolated system via cabling are a common problem for sensitive instruments. Cables can carry vibrations from an auxiliary piece of equipment (such as a pump or fan) into the chassis of a sensitive instrument. Cables can also transmit noise — vibration, acoustic, or EMI — from walls, the ground, or other ambient sources. This is called parasitic noise.
Parasitic noise is especially troublesome because it can bypass vibration isolation systems, acoustic enclosures, and EMI cancellation systems. Since the noise is ported directly into the body of the instrument, it can be almost impossible to overcome.
Fortunately, with good cable management practices this noise can be stopped in its tracks. The most common technique to overcome cable noise is to add some weights to the cables. Any cable which is connected to a noise-generating piece of machinery should be carefully weighted. Placing weight on the noise-generating equipment may also help reduce parasitic vibrations.
When the cable is being passed into a sound-proof hood, it should be clamped to the floor or to the body of the enclosure, so that the noise is diffused before it reaches the instrument. Cables that are passed into a Faraday cage or EMI cancellation system should be well grounded with conductive material to not lose their shielding qualities.
Some other best practices for cable management include:
- Ensure cables have slack in them and are not pulled taut, as taut cables transmit noise very efficiently.
- Separate and arrange the cables so they do not touch each other.
- Experiment with various weights on the cables to get the maximum noise reduction. Generally speaking, the stiffer the cable the more weight is required, but be careful: adding too much weight to a cable which transmits gas or water can create a pinch point. Too much weight can also damage certain cables.
- Looping small diameter cables and allowing them to swing freely will reduce parasitic vibrations.
- For large diameter cables, use weights with a damping material. Select a viscoelastic material that is capable of absorbing the frequencies of concern.
For over 25 years, Herzan has partnered with electron microscopy users to enable them to achieve more from their research by removing the disruptive acoustic, vibration, and EMI noise that would affect their measurements, causing distortions to the images.
To request more information or a quotation for Herzan products, contact IL Photonics.