Datasheet

SPD series pressure sensor
last update
December 6, 2011
reference
SPD-dil family
page
3/5
Understanding the specifications
The available range of SPD series pressure sensors allows for a wide range of applications. In order to
get good results, it is very important to fully understand the meaning of the various specifications and
their effects on accuracy, especially the ones that deal with temperature coefficients. (Silicon resistors
are very temperature dependent).
Excitation voltage
The excitation of the sensor can be AC or DC. Specifications are given with a DC excitation of 5V. In
order to avoid electrical breakdown it is advised not to exceed the maximum values given.
Offset
The offset value is the electrical output voltage (imbalance) of the pressure sensor when zero pressure
is applied. The offset value for the absolute type is determined by extrapolating the measured values at
two different pressures (atmospheric air and 0.05*10
5
Pa). The pressure in reference chamber is about
3.33 Pa.
Temperature coefficients
Silicon resistors are very temperature dependent. The overall drift of the resistors is not of interest to
most users (The bridge resistors are located on the same die). The temperature coefficients of the
offset and span, however, are very important. All the temperature coefficients are given in percentage
of full-scale range (FS) and over a temperature range of 100 °C.
The maximum value of the temperature coefficient of the span is minus 27%, which means that worst
case the span becomes 27% smaller over the full temperature range of 100 °C. The offset will vary no
more than ±7% of the span over the same temperature range. For more about these effects see below
“about excitation with voltage or current”.
Calculation example (please refer to the parameter table above)
Suppose the use of a pressure sensor of type SPD 015G over a temperature range of 100 °C. The
typical full scale span is 140 mV. The offset (at a fixed temperature) will be between -50 and +50 mV.
Offset
When the static part of the offset has been nulled, the offset can still vary ±7% of 140 mV (± 9.8 mV),
over the temperature range of 100°C.
Span
The typical full-scale span is 140 mV and the typical temperature coefficient of the span equals –22
%FS/100 °C.
Typically, you would therefore have a span, which varies between 140 mV and 109 mV (140 mV minus
22%), over the full temperature range of 100 °C.
In the worst case scenario the minimum value of the span is 100 mV, which means that the sensor has
a span of 100 mV, which could drop to 63mV (100 minus 27%) over the full temperature range of 100
°C.
Linearity
The linearity is defined as the maximum deviation from the best fitted straight line.