1 Level-Module The level module can replace some other devices. The main task is the measurement of helium filling level. Controlling a heater device and caring about a hardware interlock to protect the heater against burning out is another one. The situation of the coexistence of a heater and a level meter is quite common. The level module does the task of measuring, controlling and interaction between these things. Operation / Installation The module must be installed on a DIN rail. At four existing connectors the external devices are plugged in. These are: the superconducting Sensor heater analog control heater release (contact) heater temperature sensor (TC) The module should be mounted in a way that natural thermic air movement is possible. In case of horizontal mounting active cooling is necessary. The connectors of the level module are not isolated relative to the logic and power supply.
Transcript
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Level-Module
The level module can replace some other devices. The main task is the measurement of
helium filling level. Controlling a heater device and caring about a hardware interlock to
protect the heater against burning out is another one. The situation of the coexistence of a
heater and a level meter is quite common. The level module does the task of measuring,
controlling and interaction between these things.
Operation / Installation
The module must be installed on a DIN rail.
At four existing connectors the external
devices are plugged in. These are:
the superconducting Sensor
heater analog control
heater release (contact)
heater temperature sensor (TC)
The module should be mounted in a way that
natural thermic air movement is possible. In
case of horizontal mounting active cooling is
necessary.
The connectors of the level
module are not isolated
relative to the logic and
power supply.
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LEVEL
Status sensor
Status temp.
Heater ON LED Level > Min
LED System/CPU
LED Addressing
Connection to sensor
Thermocouple Type K
Analouge output
Heater Release (Relais contact)
Figure 1: Display and connections of the Level-Module
(no function)
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1 : + U
2 : U
3 : + I
4 : I
1 : + U
2 : U
3 : AGnd
4 : prot. Gnd
1 : AGnd
2 : DC-OK
3 : AGnd
4 : + U
1
1
1
2
2
2
3
3
3
4
4
4
Initial-Resistor of
the level sensor
Figure 3: Level module, connection thermocouple at the plug
Figure 4: Level module, connection heater power supply at the plug
Figure 2: Level module, connection superconductive level sensor at the plug
+ at higher temperatures
DC-OK*
not implemented
Junction at room
temperature!
Netzgerät für Heizer
+
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Displays
Every module type has LEDs „SYS“, „ADR“ and more specific ones. SYS is yellow
during initializing. Red indicates an error. Green stands for normal operation.
Yellow/green flashing happens, when the module has been halted by the coupler after the
module has worked normally before. This happens for example if the field bus is
disconnected after having been running already.
These situations can be reasons for error indication:
- The module has a hardware error (i.e. DC/DC converter or ADC).
- The configuration requested by the module doesn’t fit to the existing one.
- The fieldbus at the coupler is not supported by the module.
Errors are read by the coupler and can be sent to the control system.
The ADR LED indicates the status of addressing. Yellow: Address is to be determined,
green: address found, red: conflicting addresses. Only if a correct address could be found
data communication over the internal CAN bus can take place.
The remaining LEDs show the status of the level sensor, the heater and the thermocouple
at the heater. Additionally there is a LED which shows that a minimum of liquid helium
is in the containment.
LED sensor (S)
Green: Normal operation in cold environment.
Green flashing: Sensor is being activated.
Red: Sensor is switched off in warm environment.
Red flashing: Sensor has an error. Check status bits.
Dark: Sensor is switched off.
If measuring has not yet started, green means ‘sensor is OK’. After switching on the
sensor current the LED is flashing green until getting stable level readings. When the
sensor is switched off (since V1.4) it is tested in the beginning and when its plug is
connected. The result is displayed for a second as red (error) or green (ok) light.
LED thermocouple (T)
Blue: Heater is cold enough to be switched on.
Red: Heater is still too warm, no release.
K1
1
2
3
4
Figure 5: Level module, connection heater power release at the plug
0V +24V
Line
1 : n.c.
2 : n.c.
3 : Rel Com
4 : Rel. NO
K1
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Red flashing: The thermocouple has an error.
LED thermocouple (T) when simulated (see chapter about DIP-switch)
Blue flashing: Simulation correct. Temperature release permanently granted.
Red flashing: Error.
LED heater (H)
Green: Heater release (relay output) ON.
Dark: Heater OFF.
Green flashing: The relay has an error.
LED filling level (LEV)
Blue: Minimum level reached (a release condition of the heater).
Dark: No filling level release.
How the Filling Level Measurement works
The sensor for measuring the filling level mainly consists of a thin wire which becomes
superconducting at temperatures in a helium bath. For production a niobium titanium
wire (NbTi) is used which has a thin copper layer on the surface. This is good for to be
soldered easily. In contrast to the production of superconducting magnet coils the copper
layer is not desired. In case of a quench this layer shall not take over the current in the
conductor but the relative high resistance of the alloy in normal conducting state is
needed for the measurement principle. Therefor the copper is removed by etching after
soldering. During measurement the wire is mounted vertically in the helium bath. In the
area of helium gas the thermally coupling between the wire and the cold environment is
so bad, that the current through the wire heats it above the transition temperature of about
9 Kelvin. In the fluid the wire keeps cold. In the area of transition the right choice of the
current is important so that the boundary to the superconducting area is just at the surface
of the fluid and that this transition is stable.
If the temperature in the whole containment is lower than the transition temperature, the
whole wire is superconducting. When switching on the current nothing would change
because no heat is dissipated. Therefor a normal resistor is soldered on the upper end of
the wire which heats up and initiates a quench by the thermal contact with the measuring
wire. This quench propagates down until it reaches the surface of the liquid. During the
wire heats up a little in the gas area, the resistance is still going up a little until it is
reaching an equilibrium. The level module considers this by waiting for this equilibrium
in the beginning or after a break in measurement. A quench propagation speed of at least
7.8 inch/second is assumed. As soon as the resistance does not become more between two
measurement cycles the module changes to normal operation. During stabilization the
green sensor-LED is flashing. If this phase ends because of a timeout the LED is flashing
red shortly in the end. During operation this LED is green. If the resistance is bigger as
the resistance of the wire in cold gas, it is assumed that the containment is warm. The
sensor will be switched of and the LED lights red in this case. For this mechanism it is
necessary that the active length and the specific resistance of the wire at 20 K have been
provided correctly. In extreme cases the sensor could be destroyed when the wire is
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loaded in vacuum and the warm state could not be recognized because of wrong
parameters.
Parameterization
The bus master is sending configuration data as well as parameters of the connected
modules over the field bus. At DESY these data are built using the I/O configurator
which has access to the device database. The choices (menus) and default values are
taken out of the GSD file for the ‘Kryo-I/O-System’.
These parameters must be set:
Minimum level for releasing the heater.
Specific resistance of the sensor wire (11.4 /inch AMI standard)
Units of active length (cm or inch)
Sensor operating current (2K-sensors 53.1mA, 4K-sensors 75mA)
Heater analogue control (without, 0..2V, 0..2.5V or 0..4V)
Active sensor length (units as chosen before)
Correction
The correction value is left zero in the beginning. If all parameters are set according to
the data sheet of the manufacturer of the sensor and in cold empty reservoir the level
module does not show 0% the correction can be made. At cold empty tank the level
value is noted. This is our variable h0.
The correction parameter K computes as follows:
K1 = h0 / (100 - h0)
Input of the correction in per mille: K = 1000 * K1
Example: Display value -1.3%
K1 = -1.3 / (100 – (-1.3)) = -0.01283..
K = -0.01283 * 1000 = -13 (rounded to the nearest integer number)
After K has been set as the correction parameter and after rebooting the IOC (fieldbus
master) the level value will show the right value.
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Address and Data Layout The base address results depending on position and type of plugged-in modules (separate
for input and output). The offset addresses of process value positions are organized as
