2 Temperature Monitoring Sensors
Temperature monitoring of containment shroud
Eddy currents are induced in the metal containment shroud walls of mag-drive
pumps. This causes the metal containment shroud to heat up. The heat loss
generated is dissipated by a secondary circulation flow. The source of the cooling
flow for the rotor space can be internal or external.
▪ With internal circulation, the cooling flow is bypassed from the main flow. The
main flow passes through the pump's hydraulic system.
▪ With external circulation, the cooling flow is supplied to the rotor space from the
outside via auxiliary connections.
Potentially explosive atmosphere
The cooling flow is sufficiently dimensioned for intended operation. The maximum
permissible surface temperature that is dictated by the temperature class to
EN13463-1 is not exceeded (temperature class and maximum permissible operating
temperature as specified in the data sheet). An impermissible rise in temperature can
occur at the containment shroud when the cooling flow is insufficient or fails
completely.
An insufficient cooling flow or failure of the cooling flow can be caused by the
following:
▪ Fluid properties
▪ Pressure too low
▪ Desynchronisation of magnetic coupling
The maximum surface temperature occurs at the containment shroud tube in the
magnetic coupling area. KSB offers the following measuring instruments to detect an
impermissible increase in temperature at the containment shroud:
▪ PT100 resistance thermometer
For design and operational reasons, the PT100 resistance thermometer cannot
detect the maximum surface temperature that occurs at the containment shroud.
It can monitor the operating status of the pump. A distinction is made between
the following operating statuses:
–
Intended operation: Temperature at containment shroud OK
– Failure: Temperature at containment shroud too high
▪ Mineral-insulated thermocouple
The mineral-insulated thermocouple can be used to monitor the temperature in
this area.
2.1 Temperature monitoring at the containment shroud via the PT100
resistance thermometer
2.1.1 Function
Resistance thermometers are temperature sensors that measure the change in
electrical resistance of metals with changing temperature. Resistance thermometers
use a very thin layer of platinum film on a ceramic substrate. The nominal resistance
of these measuring elements at 0 °C is 100 ohms.
Interpretation of readings
The nominal resistance of the PT100 resistance thermometer at 0 °C is 100 ohms.
Equation for calculating the resistance value at any temperature (T):
Temperature range: T = 0 - 850 °C
R (T) = 100+0.39083×T -5.775×10
-5
×T
2
2 Temperature Monitoring Sensors
Monitoring Systems
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