IBM is a trademark of the International Business Machine
Corporation.
MS-DOS and Windows are trademarks of the Microsoft
Corporation.
Other product names used in this document may also be
trademarks and are only used for identification purpose.
Before using the instrument for the first time in a hazardous location:
Observe all the safety instructions in these operating instructions.
1.2Essential safety notes for the MLA 900
b
Observe the following safety notes when assembling and operating the instrument,
during maintenance and repair, and when exchanging parts – for your own protection.
The most important safety rules are:
VORSICHT: Risk of wrong measurements
b
Before using the MLA 900: carry out a performance test (→S. 21, §4.3) –
always to be done outside of the hazardous locations.
WARNUNG: Hazard when potential equalisation is missing:
b
Before the measuring probe is lowered into the liquid container: Safely
connect the ground clamp of the display unit with the liquid container
(potential equalisation).
WARNUNG: Hazard when enclosure is open
b
Never open the instrument enclosure as long as it is in a hazardous
location.
WARNUNG: Hazard by unsafe instrument
b
If there is any reason to assume that the instrument is no longer safe: shut
down the instrument and protected it against unauthorised use.
The MLA 900 determines the electrical conductivity and the temperature of petroleum
products such as occur, for example, in aviation fuels and in other petroleum products.
During the filling process, pumping or filtering, these liquids may become electrostatically
charged. If, in addition, there is an inflammable gas mixture present in the ambient
atmosphere, there is a danger that the gas mixture will be ignited by a discharge spark,
which means that it may explode. To evaluate this risk, the electrical conductivity of the
liquid is measured (see German standard DIN 51 412-T02-79, »Determining electrical
conductivity, field procedure«).
The conductivity is stated in the physical unit »pS/m« (picosiemens per meter). This unit
corresponds to »c.u.« (conductivity unit), which is still commonly used in the petroleum
industry:
Ambient conditions
The MLA 900 is designed as a measuring instrument for outside use.
b
Use the MLA 900 at an ambient temperature of –20 °C … +60 °C (–4 … +140 °F).
Outside this temperature range it can no longer be guaranteed that the instrument will
function correctly.
pS
1
1c.u.=
m
● At temperatures above +60 °C (140 °F) there is a danger that caustic liquid
from the battery may escape and damage the electronics. Apart from this,
the LC displays may be damaged (irreversible blackening).
● At temperatures of below –20 °C (–4 °F), the LC displays in the display unit
may freeze, resulting in the LC display enclosure bursting.
● Low temperatures affect the flexibility of the probe cable.
b
Avoid bending the probe cables in low temperatures.
Otherwise the probe cable could brake due to the sheath becoming brittle.
2.1.2Application restrictions
The MLA 900 may only be used to measure the conductivity and temperature of petroleum
products, such as petrol, kerosene and oils/greases. Other liquids such as acids or
solvents containing chlorinated hydrocarbons, for example, can damage the measuring
probe.
● German standard DIN 51 412-T02-79 (»Determining electrical conductivity, field
procedure«)
● ASTM 02624 »Standard Test Methods for Electrical Conductivity of Aviation and
Distaillate Fuels«
The technical design of the MLA 900 corresponds to:
● European standard EN 60079-0:2006
● European standard EN 60079-11:2007
● European standard EN 60079-26:2007
● European Council Directrive 94/9/EC (ATEX guideline)
● German »Ordinance on electrical appliances in hazardous locations« (»Verordnung
über elektrische Anlagen in explosionsgefährdeten Räumen«, ElexV) of 13 December
1996.
2.2Official approval
2.2.1Definitions of terms
● An explosive mixture is a mixture of gases, vapours, mists or dusts in which a reaction
continues independently after ignition.
● An explosive atmosphere contains explosive mixtures of gases, vapours, mists or dusts
with air, including usual admixtures (for example, humidity) under atmospheric
conditions. Atmospheric conditions are here defined as total pressures of 0.8 to 1.1 bar
and gas mixture temperatures of from –20 °C to +60 °C.
A dangerous explosive atmosphere occurs when in the event of an ignition injury may
be caused to persons as a direct or indirect result of the explosion.
● Hazardous locations are those areas in which a dangerous explosive atmosphere may
occur due to local and operational conditions.
Hazardous locations are divided into zones on the basis the probability (in terms of time
and place) of the presence of dangerous explosive atmospheres:
– Zone 0 includes areas in which a dangerous explosive atmosphere is present
»constantly or for longer periods«; for example, in tank facilities.
– Zone 1 covers areas in which a dangerous explosive atmosphere »occasionally«
occurs; for example, in the vicinity of refuelling nozzles.
The MLA 900 is approved for use in hazardous locations in which inflammable gases,
vapours or mists may occur (EEx ia IIB T6). The MLA 900 measuring probe is approved for
use in Zone 0, the display unit for use in Zone 1.
Prescribed operating conditions
The following applies for the use of the MLA 900 conductivity meter in the area of
application as defined in the »Ordinance on electrical appliances in hazardous locations
(ElexV)«:
WARNUNG: Hazards in explosions-hazardous locations
● The MLA 900 is intended exclusively for mobile use at different locations.
● The measuring probe of the MLA 900 is approved for use in containers for
inflammable liquids (Hazardous Location Zone 0).
● The display unit of the MLA 900 may only be used in Hazardous Location
Zone 1.
● The measuring probe may only be used in such liquids against which the
→
materials of which it is made offer adequate chemical resistance (
§2.1.2).
● Damaged measuring probes may not be used in Zone 0.
● Before the measuring probe is taken to Zone 0, all plug and threaded cable
connections must be checked.
● The measuring probe may only be used with the appropriate display unit.
● Before the measuring probe is lowered into the liquid container (tank), the
ground clamp of the display unit must be connected to the container to
equalize the electric potentials.
● Tight bending may damage the cable (cable breaks).
● Damaged cables must not be used in hazardous locations.
b
Never buckle the probe cable and do not bend the cables too far.
b
At temperatures below 0 °C (32 °F), treat the probe cable with particular
care – because the cable sheath may become brittle at these temperatures.
Avoid tight bending (risk of breakage).
Bild 1MLA 900 supply schedule
ground clamp
● Keep the transport box even if you do not wish to use it when operating the
● List of spare parts
display unit
probe cable
2m
MLA 900. It may be useful as a shipping packaging.