VibroSystM 797L User manual

Copyright © VibroSystM Inc., 2006 1
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797L Piezoelectric Accelerometer_Installation Manual_Table of Contents - Rev. 1
797L Piezoelectric Accelerometer
Installation Manual
(Product # 9400-09M3A-101)
This manual divides into the following sections:
Section 1: Installation of the Piezoelectric Accelerometer and Cable
Section 2: Datasheet:
•797L Piezoelectric Accelerometer

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797L Piezoelectric Accelerometer and Cable_Installation - Rev. 1
INSTALLATION OF 797L PIEZOELECTRIC ACCELEROMETER AND CABLE
Preliminary considerations
•The 797L piezoelectric accelerometer is a solid-state device
with an isolated piezoceramic sensing element capable of
detecting low to mid-level displacements in the same axis as the
mounting hole on slow to medium speed machines. It contains
no moving parts and can be oriented in any direction.
•Operates under most harsh environmental conditions.
•Unaffected by dirt, oil, and most chemical atmospheres.
•The piezoelectric membrane minimizes the effects of transverse
motion, base strain, and thermal transients.
•The flat frequency response is from 1 Hz to 500 Hz.
•The mounting location must be chosen according to application. Absolute shaft vibration measurement
applications will require that the accelerometer be mounted on the same support structure and in the
same axis as the proximity probe.
•The 797L piezoelectric accelerometer is shipped with a captive screw for stud mounting. In selecting
mounting location, pay attention to accessibility.
•The accelerometer must in most cases directly contact the machine surface.
•The closer the contact is between the accelerometer and the machine, the better the ability to couple and
measure high frequency signals. Best efforts must be made to provide a flat, smooth, and even mounting
surface by spot facing the location. The tapped hole must be perpendicular within 1°to the mounting
surface.
•Avoid mounting the sensor on thin sections or vibration-free areas.
•Excessive mechanical shock from hard impacts can destroy the internal electronic components or
fracture the piezoelectric crystal. Avoid dropping the accelerometer.
If the accelerometer is installed on an insulated bearing, a nonconductive mounting
support must be used to preserve the integrity of insulation.

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797L Piezoelectric Accelerometer and Cable_Installation - Rev. 1
ACCELEROMETER INSTALLATION
Supplies needed:
•Mounting screw 1/4-28 UNF or M6x1
•Loctite 222 thread adhesive
Tools needed:
•Drill bits 7/32’’ or 5mm
•Tap drills 1/4-28 UNF or M6x1
•Torque screwdriver
Caution: Use great care in handling the Model 797L accelerometer. NEVER DROP it or hit it against a
solid object. Keep it stored in its box until you have surveyed and prepared the location suitable for
installation.
Step 1) Preparation of the mounting area
1. Select the best mounting location according to your application (refer to preliminary considerations).
Prepare the surface and mounting hole according to Figure 1 a) if the screw has UNF thread or Figure
1b) if the screw has a metric thread.
Figure 1
a) b)

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797L Piezoelectric Accelerometer and Cable_Installation - Rev. 1
Step 2) Mounting the accelerometer
1. Mount the accelerometer using a torque screwdriver for tightening. The supplied captive screw should be
torqued to a nominal value of 3,3895 Nm (30 lb-in). Under-torquing the accelerometer reduces the
stiffness of the coupling, while over-torquing can cause permanent thread damage.
Note: Use Loctite 222 thread adhesive for better results.
Installation on an insulated bearing
1. Shown here is an alternate mounting
method. The sensor is installed on an
insulating block.
If the sensor is installed on an insulated bearing, special care must be taken to
preserve the insulation of the bearing.
The most widely recommended mounting method consists in placing a 0.063 in.
thick mica sheet between mounting bracket and bearing, and using non-metallic
screws.

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797L Piezoelectric Accelerometer and Cable_Installation - Rev. 1
2. Glue is applied on the block and
insulated surface.
3. The sensor is held in place until the
glue has set. The sensor can be
mounted vertically or horizontally.

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797L Piezoelectric Accelerometer and Cable_Installation - Rev. 1
CABLE INSTALLATION
Preliminary considerations
•This twisted pair, shielded, yellow teflon cable is 5 m (16 ft.) long
and will run between the piezoelectric accelerometer and the
PCU-100 Unit.
•In applications of 500 Hz maximum frequency such as the ones
this accelerometer is designed for, the cable capacitance of 30 pF
per foot allows the cable to run over a total length of 100 m (330
ft.). For applications involving a cable longer than 5 m (16 ft.), a
tapping box is needed.
•The cable should be enclosed in a protective conduit.
Step 1) Installation of the cable
1. Determine the run of the cable, keeping in mind that its maximum length is 100 m (330 ft.).
2. Unroll the protective conduit following the planned course of the cable. Cut the conduit to desired length.
3. With a fish tape, carefully pull the cable into the conduit. The socket connector must be placed on the
accelerometer side.
4. Connect the cable to the accelerometer.
5. Anchor the cable to reduce stress at
the cable terminations. When
securing the cable, leave enough
slack to allow free movement of the
accelerometer as shown in Figure 2.
Figure 2
Step 2) Connection of the power and output cable
1. Connect the wires according to the following designation:
PIN # WIRE COLOR DESIGNATION
A White Power/signal
Shell Shield Ground
B Black Common

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797L Piezoelectric Accelerometer and Cable_Installation - Rev. 1
a) Uninsulated bearing
The housing of the accelerometer is connected
to ground: do not connect the cable shield-to-
ground at the monitored end.
Figure 3: Uninsulated bearing
b) Insulated bearing
The housing of the accelerometer is isolated
from ground: connect the cable shield-to-ground
at the monitored end.
Figure 4: Insulated bearing
Step 3) Verification
1. Verify that the 797L piezoelectric accelerometer is functioning well: measure the voltage at the output of
the accelerometer (e.g. between black and white wires, at input of the PCU-100 unit). Note that the warm-
up time is about two minutes. The bias voltage (or voltage at rest) should be about 10 VDC (+/- 1v).
2. Much lower or higher DC bias voltages indicate internal problems and the accelerometer should be
carefully packed and returned to the factory for repair.
Figure 5: Vibrations to bias voltage
Vibrations t
Bias Voltage = 10VDC