Instructions for Use
– SCHMIDT
®
Flow Sensor SS 20.700
Page 26
Exceeding measuring range of flow velocity w
N
Measuring values larger than w
N,max
are output in a linear way up to
110 % of the signaling range (this corresponds to 11 V resp. 21.6 mA,
see graphics in Table 8). At higher values of w
N
, the output signal re-
mains constant.
Error signaling does not take place because damaging of the sensor is
unlikely.
Medium temperature T
M
outside specification range
Operation beyond the specified limits can damage the sensor and,
therefore, is seen as a critical error. This leads to the following reaction
depending on the temperature limit (also refer to graphics in Table 9):
o
Medium temperature below T
M,min
= -20 °C:
The analog output for T
M
switches to error (0 V or 2 mA)
24
.
The measuring function for flow velocity is switched off, its analog
output also signals an error (0 V resp. 2 mA).
o
Medium temperature above T
M,max
= +120 °C:
T
M
is output in a linear way up to at least +125 °C, flow velocity is
measured and displayed further on.
Above this critical limit, flow measurement is switched off and the
analog output w
N
switches to error signaling (0 V or 2 mA).
The signal output for T
M
, on the other hand, jumps to the maximum
values of 11 V resp. 22 mA, in contrast to normal error signaling.
This is to avoid a catastrophic feedback if a heating control uses the
medium temperature sensor of the
SS 20.700
. The standard error
signal (0 V or 2 mA) could be interpreted by the control as a very
low temperature of the medium which would consequently lead to
further heating.
24
The switching hysteresis for the threshold is approx. 5 K.
