Specifications

METTLER TOLEDO Weigh Module Systems Handbook

(12/99)

5-24

Home Run Cables

A home run cable transmits the summed load cell signal from the junction box to

the indicator. To provide accurate weight readings, a scale must be able to

distinguish between electrical signals that differ by millionths of a volt. So small

amounts of noise introduced through the cables can cause weighing errors.

Common sources of noise are radio frequency (RF) and electromagnetic (EM)

radiation produced by power cords, power lines, motors, or cellular phones.

To reduce radio frequency and electromagnetic interference, install a ferrite ring

over the home run cable at the indicator. It should be placed inside a harsh

enclosure or as close as possible to the connector on a panel-mount enclosure.

Wrap the home run cable conductors and the shield ground wire around the ferrite

ring four times (see Figure 5-30). Keep the ferrite ring as close as possible to the

point where the cable enters the enclosure.

To Ground Stud

Shield Ground Wire

Four Turns

Ferrite Ring

Load Cell Cable

Grip Bushing

Figure 5-30: Ferrite Ring Apparatus

The following installation guidelines will also help prevent electrical interference:

• Install cables at least 12 inches from power lines.

• Fully insulate and ground cables to prevent them from picking up unwanted

noise.

Cables are often exposed to mechanical damage or damage caused by water or

chemicals. To protect cables from damage, encase them in flexible conduit. Teflon

coatings are available to protect cables in corrosive environments. If a mixing

agitator is attached to a tank, keep enough slack in the power supply cables to

prevent live-to-dead load interference.

Home Run Cable

Junction Box