Download Load Cell Troubleshooting

Test #1
Zero Balance
Test #2
Insulation
Resistance
OK
VPG-08
OK
Te
Br
Inte
VPG Transducers
Wrong
Wrong
Load Cell Troubleshooting
TEST PROCEDURES AND
ANALYSIS
Mechanical
Moisture
or
chemical
overload
Test Procedures
andfor
Analysis
The diagram below represents a proposed
sequence
testing load cells after
a particular system
ingress
thea proposed
fault location
byfor
moving
relatively
deadweight
over each load
cell,
The malfunction.
diagram below Isolate
represents
sequence
testing a
load
cells aftersmall
a particular
system malfunction.
Isolate
the
faultor
location
by moving a relatively
small
by disconnecting
load cell
by deadweight
load cell. over each load cell, or by disconnecting load cell by load cell.
R1kΣ
Sudden change
in Zero point
Unstable readings,
random change
in Zero point
Scale reads overload,
incorrect or not at all
Erratic readings
when load is
appliedcircuit
or removed
Short
Brok
or com
to housing / screen
Test #1
Zero Balance
Test #2
Insulation
Resistance
OK
OK
Test #3
Bridge
Integrity
OK
TEST #1: ZERO BALANCE
Wrong
Mechanical
overload
Test #4
Shock
Resistance
Electrica
or in
shor
OK
Wrong
Wrong
The Zero
Balance is defined
as the load Wrong
cell output in a "no-lo
deadload)
has to beElectrical
removed
from the load
cell. Low capacity load c
Moisture
overload
Failed electrical
or
chemical
or
internal
connection
the ingress
load cell is designed
to measure force to prevent the weight of the
short circuit
The load cell should be connected to a stable power supply, preferab
R≤1
kΩ
R∞
R1kΣ
R4
of at least 10 volts. Disconnect any other load cell for multiple load c
Measure
across
Short circuit the voltage Broken
wire the load cell's output leads with a milli
to housing / screen
or component
excitation voltage to obtain the Zero Balance in mV/V. Compare the
certificate ( if available ) or to the data sheet.
Test #1: Zero Balance
TEST #1: ZERO BALANCE
A PPL I CAT I O N N OT E
The Zero Balance is defined as the load cell output in
Input
The Zero
BalanceTherefore,
is defined all
as weight
the load(including
cell output in a "no-load" situation.
Therefore, all weight (including
a "no-load"
situation.
deadload)
has has
to be
removed
from
Lowcapacity load cells should be measured in the position in which
deadload)
to be
removed
fromthe
theload
load cell. Low
~
capacity
cellsisshould
be to
measured
thetoposition
the load cell
designed
measure in
force
preventin
the weight of the element giving wrong results.
whichThe
the load
load cell
cell should
is designed
to measure
topower
prevent
be connected
to aforce
stable
supply, preferably a load cell indicator with an excitation voltage
the weight
of
the
element
giving
wrong
results.
of at least 10 volts. Disconnect any other load cell for multiple load cell systems.
Measure
the voltage
across the
cell's
output
leads with a millivoltmeter and divide this value by the input or
The load
cell should
be connected
to aload
stable
power
supply,
excitation
voltage
to obtainwith
the Zero
Balance involtage
mV/V. Compare the Zero balance to the original load cell calibration
preferably
a load
cell indicator
an excitation
( if available
) or toany
the other
data sheet.
of at certificate
least 10 volts.
Disconnect
load cell for
Output
multiple load cell systems.
V
Measure the voltage across the load
cell's output leads
Input
with a millivoltmeter and divide this value by the input ~
or excitation voltage to obtain the Zero Balance in mV/V.
Compare the Zero balance to the original load cell
calibration certificate ( if available ) orANALYSIS
to the data sheet.
zero output changes per time period are most likely
in the
strain gauge
resistance
Changes in Zero undergoing
Balancea change
usually
occur
if the
loadbecause
cell has been
Analysis
Output
of chemical or moisture intrusion. However, in this case
excessive shocks.theLoad
cells that experience progressive zero ou
insulation resistance and/or the bridge integrity will
Changes in Zero Balance usually occur if the load cell
also be
has been permanently deformed by overloading
and/or
undergoing
a change
incompromised.
the strain gauge resistance because of chem
excessive shocks. Load cells that experience progressive
the insulation resistance and/or the bridge integrity will also be comp
ANALYSIS
V
Changes in Zero Balance usually occur if the load cell has been permanently deformed by overloading and/or
For technical
support, contact
in Americas
www.vpgtransducers.com
Document
Number:
11867
excessive shocks. Load cells
that experience
progressive
zero [email protected],
output changes per time period
are most
likely
in Europe
[email protected],
in China
[email protected],
2
Revision
undergoing a change in the strain
gauge
resistance because
of chemical
or moisture intrusion. However,
in14-Dec-2011
this case
in Taiwan [email protected]
the insulation resistance and/or the bridge integrity will also be compromised.