Install ferrites

Note: The accelerometers are shipped with ferrites installed at the accelerometer end. To maintain the optimum performance of the accelerometer, do not remove the ferrites.
To meet the stated performance criteria, the standard accelerometer cable has two (2) ferrites installed. These are Steward ferrites (P/N 28B0355-000), with each providing 205 Ω of reactance at 100 MHz.

Figure 1. Standard accelerometer cable with ferrites installed (as shipped from the factory)



The armor-jacketed accelerometer cable has one ferrite installed. It is a Steward ferrite (P/N 28B0672-000), which provides 245 Ω of reactance at 100 MHz.

Figure 2. Armor-jacketed accelerometer cable with ferrite installed (as shipped from the factory)



If your cables require additional immunity after accelerometer installation is complete and accelerometer cables have been run through a conduit (if applicable), you can place additional ferrites on the other end of the cable.

Note: The performance of the accelerometer is not maintained beyond a 3-m (10-ft) cable-length unless you install additional ferrites.

All low-power sensors for use with the CSI 9420 are shipped with additional ferrites if their cable lengths exceed 3 meters. To ensure compliance with the CE directive, if the cable length exceeds 3 meters, all standard sensor configurations (1 accelerometer, 1 accelerometer with embedded temperature, or 2 accelerometers) require ferrite installation at the site.

These ferrites are not installed on the accelerometer cable at the factory because they must be installed on the transmitter end of the cable, and the cables are typically cut to length at the site. To maintain compliance with the CE directive, sensors with cables longer than 3 meters must have 3 additional ferrites installed. You do not need to install the additional ferrites if the cable length is less than 3 meters.

From a compliance perspective, you do not need to install the ferrites if the cable is in a ferromagnetic conduit (such as galvanized steel) because this type of conduit provides additional shielding. Note that the conduit entry of the device is ½ inch NPT. If you install ferrites with a conduit, you will need a wider conduit ( ¾ inch NPT or M20) to accommodate the ferrites and an adapter is required at the conduit entry of the device.

The ferrites provided with the sensors that have standard (polyurethane) cables are Fair-Rite P/N 0431173951. These ferrites simply snap onto the cable near the point where the cable enters the transmitter housing. You can also use wire ties and/or heat-shrink with these ferrites.

The ferrites provided with the sensors that have armor-jacketed cables are Fair-Rite P/N 2631665702. These slide onto the cable and must have wire-ties and/or heat-shrink, or some similar mechanism, to hold them in place.

Figure 3. Transmitter, accelerometer with standard cable, and ferrites (pre-installation)



Figure 4. Armor-jacketed cable and ferrites (pre-installation)



Install ferrites on a standard cable

  1. Make standard connections to the CSI 9420 terminal block and grounding screw.
  2. Snap the first of three attenuator ferrites (MHM-94985) at the location on the cable approximately 1 in. from the point where the cable enters the gland.
  3. Snap the second ferrite onto the cable adjacent to the first; then snap the remaining ferrite adjacent to the second.
    Note: Apply adequate force in the ferrites' closures so that the keeper latches fully engage. This ensures that the ferrites remain securely fastened to the cable.

Figure 5. Ferrites installed on a standard cable



Install ferrites on an armor-jacketed cable

  1. Make standard connections to the CSI 9420 terminal block and grounding screw.
  2. Slide the first of the three ferrites at the location on the cable approximately 1 in. from the point where the cable enters the gland.
  3. Secure the ferrite using a wire tie, heat-shrink, or any other method approved for your location.
  4. Slide the second and third ferrites onto the cable adjacent to the first, and secure them in place with a wire tie or heat-shrink.

Figure 6. Ferrites installed on an armor-jacketed cable



You need an additional ferrite for devices that use external DC supply. This ferrite is included with the transmitter if you order the external power option.

Figure 7. Transmitter using an external power option with ferrites installed



This is a snap-on ferrite. Depending on the size of the wire used, you might need to secure the ferrite in place.

The ferrite in this example is Fair-Rite P/N 0431164281, which has a reactance that ranges from 28 Ω at 1 MHz to 310 Ω at 100 MHz and 240 Ω at 250 MHz. It supports a maximum cable diameter of 0.260 inch (6.6 mm).

Effect of ferrites on interference

Figure 8 compares two accelerometers in the presence of a high-intensity RF field (10 V/m). The oscilloscope is the time-domain representation of the signals.

The upper trace (A) is a standard (non-armor-jacketed) 3-meter cable, without conduit, with polarization matching that of the interference field, and with two ferrites installed at the accelerometer end of the cable. The resulting interference is about 10 mV peak-to-peak, which is equivalent to a perturbation of about 0.2 g's peak to the acceleration measurement.

The lower trace (B) is a 3-meter cable of the same type, without conduit, with polarization matching that of the interference field. In this case there are no ferrites installed, and the resulting interference is about 1.2 V peak-to-peak, which is equivalent to a perturbation of about 24 g's peak to the acceleration measurement.

Figure 8. Accelerometer signals in the presence of high-intensity interference with and without mitigation*

  1. With two ferrites installed
  2. Without ferrites installed

*Scale is not the same for A and B in this graph.



Figure 8 also shows that ferrites provide a huge amount of RFI suppression and are needed to maintain measurement integrity in the presence of strong electromagnetic interference. Do not remove the ferrites installed on the accelerometer cables that are shipped from the factory, even if you mitigate interference using other methods.