MTL Instruments LC30 Specifications

• Protects load cells, weighbridges,

process weighing and silos

• Certified for use in legal metrology

applications

• Reliable, high surge absorption

capacity

• Easy filed installation in rugged

weatherproof enclosure

• Can be used in intrinsically safe

circuits without further certification

technical datasheet

LC30

Protects load cells and electronic weighing equipment against surges
and transients on system cabling

The LC30 surge protection device
protects load cell and weighing system
installations from possible malfunctions

or damage to individual strain-gauge bridges
of associated electronic instrumentation etc.
caused by severe overvoltages or impulse
currents on signal cabling.

Weighbridges, silos and other product
batching/weighing facilities are typically

large metal structures, and are exposed
to direct lightning strikes. Protecting the
structure from lightning is not in itself
sufficient to prevent the secondary damage
to associated electronic systems. Individual
load cells and strain-gauge bridge insulation
may break down under the abrupt shift in
local structural voltage as lightning currents
are dissipated to local ground, thus allowing
surge currents to flow through the connecting
cable into the various indicators and power
supplies situated some distance away.
The connecting cabling can be armoured,
shielded, underground and may still be
susceptible to surges.

Load cells may be damaged by surges,
as few transducer manufacturers make
more than a token effort at incorporating
protection components. Adequate protection
is even more critical with digital load cells,
where electronic components and amplifiers
are installed right at the point of greatest
exposure.

Surge protection devices protect the
system at the point of installation, therefore
a full system is likely to have at least one
LC30 device installed at the weighbridge to
protect the load cell(s), and another LC30
in the weighing control cabin to protect the
electronics installed there.

Fully solid-state, the LC30 clamps
incoming surges immediately without
causing undue leakage losses under normal
conditions. Once the surge has passed, the
device automatically resets to the passive
state, allowing normal operations to continue.
The advanced protection concept used in the
LC30 also eliminates the expensive additional
earthing systems specified by other suppliers,
so field installation is very simple indeed.

The LC30 can be used in hazardous
area applications with appropriate self

generated system documentation as it is
non-voltage producing, non energy storing
‘simple apparatus’. Our application guide
details the steps necessar y to achieve an
intrinsically safe installation. The LC30 is
designed for use in Zone 2/Div2 and is also
suitable for legal metrology applications.

901-113 Rev E 160210

www.mtl-inst.com [e-mail]

SPECIFICATION

All figures typical at 77°F (25°C) unless otherwise stated

Maximum surge current

10kA

Leakage current

10µA at 32V dc

Limiting voltage

80V (after 6kV/3kA IEC 61000-4-5
combination wave test)

Nominal excitation voltage

20V ac or dc

Maximum excitation voltage

22V ac or 32V dc

Protection

Dust and watertight to IEC 60529:IP67,
GRP enclosure

Ambient temperature limits

-4°F to +140°F (-20°C to +60°C) working

-22°F to +158°F (-30°C to +70°C) storage

Humidity

5 to 95% RH (non-condensing)

Connections

Input/output: 6-wire plus screen plus earth
(ground)
Max. terminal conductor size

1.5mm2 (15 AWG) Glands (IP68) provided
for cable sizes 5 to 10mm dia. Main earth
connection; M8 external stud Mounting
Internal 0.28” (7mm) dia. through-holes

Weight

3.3 lb (1.5kg)

Dimensions

See figure 1

EMC Compliance

To generic Immunity Standards, EN50082,
part 2 for industrial environments

Figure 1 Dimensions

Figure 2 Typical weighbridge system connections

INSTALLATION

The LC30 should be located close to the load
cell or system being protected, preferably
within 3 metres. For maximum protection,
LC30’s should be used at both ends of
the interconnecting cable. Generally, one
protector is installed between the field
summation box and load cell groups. Some
systems specify individual cables per load cell
and therefore one protector at each load cell
is required.

Once the location of surge protection has been
established, it is essential to ensure correct
earthing of the surge protection devices.
No specific grounding rods are necessary
around the weighbridge; the normal earthing
of the structure is more than adequate.
When protecting equipment the LC30 surge
protection device should be bonded to the
equipment earth with the minimum length of
cable possible. Both ‘earthed’ and ‘isolated’
screen connections are provided, so that
the normal practice of any particular load
cell supplier (with respect to screens) can be
maintained. LC30(s) should also be used at
the weigh cabin for signal wiring and a mains
protector should also be fitted to the mains
supply.

Figure 3 Typical connection at load cell

Approvals

Authority Standard

NMi Certified in accordance with EN45501, NMi certification number TC2720,

based upon OIML R60

Test results demonstrating complete system accuracy in accordance with OIML R60 can be
provided. The LC30 has been tested and certified in accordance with paragraph 8.1 of EN45501
(derived from OIML recommendation R76) by NMi (Nederlands Meetinstituut) for use on non­automated weighing systems, and can be used for legal metrology on systems using R60
approved loadcells. The UK National Weights and Measures Laboratory (NWML) will approve the
use of the LC30 in UK “pattern” approved weighbridges meeting the required characteristics.

The given data is only in tended as a product des cription and should not b e regarded as a legal warranty o f properties
or guarantee. I n the interest of fu rther technical develop ments, we reserve t he right to make design changes.

EUROPE (EM EA): [phone] THE AMER ICAS: [phone] ASIA-PACIF IC: [phone]

[e-mail] [e-mail] [e-mail] 901-113 Rev E 160210