DELTA M Corporation
3242-OM-04 3/27/02
4
SIGNAL
VACUUM
AIR
HYDROCARBON LIQUIDS
WATER
LIQUID METALS
MEDIA
D
E
C
R
EASI
N
G
T
H
E
R
MAL
D
ISPE
RS
IO
N
OR
H
E
A
T T
R
AN
SF
ER
0
DRAWING FILE: MTF2A0.DWG
2.1 Level
Switching
The thermal differential created between the heated and reference unheated RTD pair is a
function of the liquid or gas medium with which the sensor is in contact.
The point level measurement application uses the heat transfer differences between two media
to detect liquid level. For example, air has a relatively poor heat transfer characteristic so the
heated sensor will become relatively hot. If the sensor is then immersed in water, the relatively
high heat transfer characteristics of water will cool the heated RTD surface causing a decrease
in the signal output.
This same rational applies for any two media in contact with the sensor. Each medium will
have its own characteristic heat transfer properties. As long as there is a reasonable
difference in the heat transfer properties between the two media, the microtuf
®
can discriminate
between them. Figure 2A shows the relative signal output of the microtuf
®
sensor to a range of
different media. The maximum difference in output occurs between vacuum and liquid metal.
However, a significant difference occurs between water and hydrocarbon liquids so the
microtuf
®
can be used to detect a water/hydrocarbon liquid-liquid interface. In general, the
interface between any two media with differing heat transfer properties can be detected.
FIGURE 2A:
RELATIVE CHANGE IN RESPONSE OF A HEATED RTD IMMERSED
IN VARIOUS MEDIA
