N°ANE120504/1
Application Note
Contents
1 Introduction 1
2 Mechanical theory
and mounting method choice 1
3 Design rules for customer’s support 2
4 Choice of fastening hardware 4
5 Screw torque 7
6 Material compatibility 8
7 Ideal LEM configuration 9
List of gures
Fig. 1: Transducer mounted on the primary
bar OR using housing brackets 1
Fig. 2: Transducer mounted horizontally
OR vertically 2
Fig. 3: First contact zone between LEM
transducer and customer’s support badly
located 2
Fig. 4: Badly designed customer’s support
effect on LEM transducer’s bracket 2
Fig. 5: Local insert effect on customer’s
support around screw head 3
Fig. 6: Insufficient contact on customer’s
support around screw head 3
Fig.7: Examples of non flat customer
support design around screw zone 3
Fig. 8: Screw axis not perpendicular to
contact surface on customer’s support 4
Fig. 9: Washer types allowed for direct
contact with LEM transducer’s brackets 4
Fig. 10: Large head screw example
integrating washer function 5
Fig. 11: Potential risk due to the use of
double washer mounting 5
Fig. 12: Loosening torque after 500 h at
23°C with self-locking system or elastic
washer 6
Fig. 13 : Torque loss with standard ISO
metric screw+flat plain washer at 23°C. 7
Fig. 14 : Corrosion effect on transducer
secondary connection with badly chosen
nuts. 8
Fig. 15 : Metals galvanic compatibility
chart. 9
1. Introduction
The aim of this document is to explain which rules the
customers have to respect when mounting LEM transducers
in their applications. Respecting the rules described below
will guarantee a good mounting of the product in its
environment and a good behavior in time.
This document only concerns mechanical mounting of
the transducers. For example, rules concerning electrical
connections, electromagnetic environment… etc are not
described here.
LEM Transducers
Generic Mounting Rules
2. Mechanical theory and mounting method choice
When a solid object has to be mounted perfectly (no possible
motion), you only have to constrain six possible movement modes,
called DOF (“degrees of freedom”). For example, defining one point
position (three translations) and orientation (three angles) enables
to know exactly the position of an object in space.
Theoretically speaking, when less than six DOFs are blocked, the
system is hypostatic and some possible motion modes remain. When
more than six DOFs are constrained, the system is hyperstatic, that
is to say, more constraints than necessary to mount the part are
used and there is a risk of over-stressing it.
In order to avoid hyperstatic problems, it’s recommended to mount
LEM transducers with only one mounting system available. Indeed,
some transducers can be mounted horizontally or vertically, using
housing brackets or primary bar mounting holes, but in each case
both mounting system shall not be used together as shown below.
No contact with customer’s plate
Primary bar fixing
points are free here
Only the 4 housing brackets
are fixed on customer’s plate
Only primary bar fixing
points are used here
The only GOOD
mounting
possibilities
Fig. 1: Transducer mounted on the primary bar OR using housing brackets
Page 2
LEM Transducers Generic Mounting Rules
Design rules
for customer’s support
3 Design rules for customer´s support
The aim of this section is to give generic rules enabling customer
to design properly the support on which the LEM transducer will be
mounted and to avoid some traps.
The main rule is to ma ximize the volume of plastic directly compressed
while tightening in order to smooth stresses. The higher the stresses,
the more important the risk of having creep phenomenon (loosening
problems of the mounting screws in time).
First of all, the support has to be as flat as possible and the contact
with the transducer has to be located primarily around the mounting
screw zones. Some interferences in other regions before screw-
tightening would cause damages on mounting brackets as shown
below (mounting bracket bending before compression due to screw
tightening) :
Another principle concerning customer’s support design is
to maximize the first contact zone between support and LEM
transducer’s bracket around screw pressure zone. The following
view shows what can happen when using a local insert lower than
general contact surface.
GOOD : First contact zone around
transducer mountin
g
brackets
BAD : First contact badly located with customer’s
base
p
late
(
initial
g
a
p
around mountin
g
brackets
)
Initial contacts
around screw
zones
Initial contact
badl
y
located
OR
Horizontal mounting
through 4 dedicated holes
designed by LEM
Vertical mounting
through 2 dedicated
holes designed by LEM
Fig. 2: Transducer mounted horizontally OR vertically
Fig. 4: Badly designed customer´s support effect on LEM transducer´s bracket
Fig. 3: First contact zone between LEM transducer and customer´s support badly located
Contents
1 Introduction 1
2 Mechanical theory
and mounting method choice 1
3 Design rules for customer’s support 2
4 Choice of fastening hardware 4
5 Screw torque 7
6 Material compatibility 8
7 Ideal LEM configuration 9
List of gures
Fig. 2: Transducer mounted horizontally
OR vertically 2
Fig. 3: First contact zone between LEM
transducer and customer’s support badly
located 2
Fig. 4: Badly designed customer’s support
effect on LEM transducer’s bracket 2