38 Ultrasound Controller Manual
The echo strength is measured and relative attenuation is calculated by comparing to the
calibrated echo strength. The relative attenuation is calculated by taking into account the
ultrasound travel distance. The result is relative attenuation measured in dB/m and it is fairly
proportionat to gel concentration. It can be converted into gel concentration. The setting of GEL-
TYPE sets the amount of gel-attenuation in dB/m at a 1% gel concentration. This value is
dependent on type of gel and the measuring frequency.
To find out the amount of gel-attenuation for your gel, you can measure it by making a 1%
concentration of the gel in a small container and using GF90 measure the relative attenuation
while intensively stirring so the gel doesn’t just fall to the bottom. (If you make another gel
concentration, for instance 3% then divide the measured gel-attenuation by 3) Then adjust GEL-
TYPE according to the gel-attenuation you have for your gel.
If you are not using GF90, it is important the ultrasound can pass as easy as possible through the
container wall. How well it passes depend on the wall material and thickness and how the Level
Switch is attached. Steel or glass wall should be in the range 1,3mm - 15 mm and plastic wall
<30mm. Testing on the actual container is recommended. Any welding-joint in the wall should be
avoided as it can refract the sound-beam.
The ultrasound beam behaves similar to a light-beam, the direction of the echo depend on from
what angle the beam hits the reflecting surface. The sound beam is approximately 1cm in
diameter. Obstructing objects in the path between sensor and the reflecting surface may cause
the beam to divert. It is possible to use objects other than the opposite container wall as a
reflecting surface. Sound also travels inside the wall along the container and this can cause
problems as it may interfer with the proper echo, especially if the echo is weak. This will be a
problem in stainless steel containers and also to a less degree in glass containers. Attaching
sound absorbing polyurethane tape outside the container near the Level Switch helps reducing
the amount of sound travelling along the containewr wall, see Level Switch Manual for more
information. This does not apply to GF90.
The Liq WR sensor measurement is done with the same sensor as the gel-measurement but is
independent of the gel-measurement. It can detect the presence of air which would otherwise give
a false indication of gel. The Liq WR sensor measures vibrations in the container wall or sensor
wall in GF90, to determine if there is air or not. The Liq WR sensor transmits sound and then
measures how vibrations in the container wall disappear. Vibrations in the wall disappear more
slowly with air. The Liq WR sensor is dependent on the material and thickness of the wall. Only
plastic wall < 30mm works well. Liq WR sensor may have some temperature dependence. The Liq
WR sensor measures small signal changes and is sensitive to small movements of the Level
Switch, therefore unless GF90 is used, gluing is preferred when using Liq WR measurement.
Mounting the Level Switch
How to mount the Level Switch on the container is described in Level Switch manual.
Gel Sensor start-screen
When power is applied, the Gel Sensor start-screen is displayed showing GelSen on first line to
the right signifying this is Gel Sensor start-screen. On the second line to the right is written 1234
which shows the state of each of the four relays. A light digit on dark signifies a closed relay.
To the left are four small digits signifying Gel Sensor 1 2 3 and 4 with three-letter-text following
each digit showing information about each Gel Sensor:
GEL gel is detected
LIQ liquid is detected
AIR air is detected
OUT measurement is near out of range (actual gel concentration can be higher than measured)
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