No. The “filament effect” suggesting that sensor amplifiers fail like a light bulb from repeated switching on and off is a myth. Piezoelectric accelerometer amplifiers are high reliability, low power devices (typical draw is less than 100 mW). The transistors used are designed for long term use in switching applications—modern transistor technology is based upon the older TTL computers that performed billions of switching operations. Wilcoxon has extensively tested the Wilcoxon PiezoFET^® in excess of two million switching operations without failure.

Yes. Multiplexing provides a convenient, cost effective way to take trend data and reduce cabling costs on permanently installed systems. Sensor turn-on time should be considered and a delay programmed into the multiplexing scheme to prevent ski slope of the first several bins of the spectrum.

Junction boxes provide a cost effective transition between walk-around data collection and permanent on-line monitoring systems. They also improve job safety by removing the data taker from dangerous environments. In addition, the signal point switchable configuration reduces labor by decreasing data collection time.

When using two conductor shielded cable from the sensor and a single barrier strip, the cable shield should be tied to machine ground through the sensor housing and terminated before the hazardous side of the barrier.

The barrier strip should be located outside the hazardous area and mounted near the junction box, multiplexer, or monitoring system. When using single barrier strips, the common signal carrier is grounded to the barrier enclosure; and therefore, must be in close proximity to monitor ground to prevent ground loops.

At the sensor, the cable should be strain relieved with enough flex to allow full movement of the machine and ease removal during maintenance. When routing the cable, both conduit and cable tie downs are used in general practice. When using tie wraps, Tefzel^® tie wraps may be required in some harsh environments such as paper machine installations.

Vibration signals from low impedance accelerometers do not crosstalk between cables in normal operation. In the rare application where very high amplitude signals are being carried next to very low amplitude signals, some crosstalk may occur. The attenuation between two conductor shielded cables in parallel contact with each other is greater than 100 dB.

In general, the cable should not be routed alongside or parallel to high current carrying wires. If the installation requires that the low signal carrying sensor cable be routed alongside the high current carrying wire, they should be separated by a minimum distance of six inches and preferably installed in a separate and grounded conduit or tray. High current carrying wires should be crossed at right angles only.

When using coaxial cables, the shield carries common and therefore, is grounded at the monitoring system. The shield must be isolated from the sensor housing to prevent ground loops.
When using two conductor shielded cable, two methods are available.

1. If the sensor housing, is electrically connected to the machine (i.e., stud mount), the cable shield is typically connected to the sensor housing and thereby tied to machine ground. In this type of installation, the shield should not be tied to the monitoring system or ground loops may develop between the monitor ground and the machine ground.
2. If the sensor housing is electrically isolated from the machine (i.e., many cement mounting installations), then the shield should be tied to monitor ground. It is recommended that the shield be isolated from the sensor housing in this type of installation to prevent ground loops in the event that the isolation between the sensor housing and the machine is lost.

Read more at https://wilcoxon.com/resources/faqs/#db4ypC3dHZAILKMI.99

Two conductor shielded is preferred for four reasons.

1. Unlike coaxial cable where the shield is a signal carrier, two conductor signal carriers are enclosed by the shield and not directly exposed to electrical interference.
2. The twist of the two conductors provides differential cancellation of magnetic interference.
3. The stripped and tinned end of the two conductors is easier to connect into terminal block panels.
4. Because the shield is isolated from the signal carriers, more advanced grounding techniques may be applied. Coaxial cables should only be used if BNC or other types of coaxial connectors are required for the installation.