Metrix ST5484E - Page 9

Doc# M9162• REV AB (April 2019) Page 9 of 12
7. INSTALLATION BEST PRACTICES FOR RFI IMMUNITY
The ST5484E is case isolated from the loop power connecon to the
PLC, DCS, SCADA, or other +24 VDC alarm system. With the correct
grounding scheme, this type of isolaon avoids ground loops and re-
sults in good RF immunity. However, in situaons which involve inter-
ference from high-powered transmiers and especially spread-spec-
trum type radios, the ST5484E may become vulnerable to RF noise.
Since it is oen dicult to idenfy these situaons in advance, Metrix
strongly recommends ulizing the following Best Pracces when install-
ing all ST5484E transmiers in the eld:
1. Twist the sensor leads together (at least 10 twists per foot).
2. Slide the twisted leads through the included ferrite core and posi-
on as close to the sensor as praccal. Refer to Figures 4 and 5.
3. If possible, cut the leads short and use a shielded twisted pair. Fol-
low step 2 in this applicaon as well.
As shown in Figure 5, “chokes” that aenuate dierent frequencies can
be created by looping a dierent number of turns through the ferrite
core. More wire turns adds more inductance, aenuang progressively
lower frequencies. Mulple “chokes” can be created in this manner
and placed in series on the wire leads to cover a broad frequency band.
Always locate the choke covering the higher frequency band closest to
the sensor.
8. CALIBRATION
The ST5484E transmier has been factory calibrated for the full-scale vibraon level marked
on the label. If the calibraon is in doubt, the unit can be veried in the eld by following
the procedures outlined below. Note that there are no Zero and Span adjustments on the
transmier. Addionally, the transmier uses a true RMS amplitude detecon circuit; units
supplied with a full scale range in peak units scale the underlying RMS measurement by a
Figure 5: Leads may also be
looped through the ferrite
core to aenuate dierent
frequencies. The opmal
number of loops will vary
by applicaon and the
interfering frequency(ies).
Figure 4: Leads may be
simply fed straight through
the ferrite core.
factor of 1.414 to provide a “derived peak” rather than true peak measurement.
7.1 Zero Vericaon
In the absence of vibraon the output current should be 4 mA ± 0.1 mA. If the ambient
vibraon exceeds 2% of full scale, the transmier should be removed from the machine and
placed on a vibraon free surface for this measurement. Oen a piece of foam can be used
to isolate the transmier from external moon.
7.2 Span Vericaon
Subject the transmier to a known vibraon within the full scale range marked on the label.
If you are using a portable vibraon shaker where it can be tested at full scale, the output
should be 20 mA ± 0.5 mA.
9. OPTIONAL DYNAMIC OUTPUT
The transmier can be ordered with an oponal dynamic output. Transmiers supplied with
this opon can be idened by the presence of four ying leads instead of two (Figure 6), or
four terminal connecons instead of two (Figure 7).
The dynamic output is an acceleraon signal with a sensivity of 100 mV/g, ltered to the