The following figure shows a typical duty cycle during autocalibration at room temperature
with 24 VDC supply voltage. Also the autocalibration current varies with supply voltage and
operating temperature.
250 mA
Duration 16 s
Duration 200 ms
0 mA
250 mA
0 mA
Figure 10 Example of Current Consumption During Autocalibration
4.5
Sampling from a Process
Sampling is needed when direct measurement of the air or gas is not possible or desirable.
This may be related to, for example, a high process temperature, protecting the sensor from
water spikes, the need to easily detach the instrument from a pressurized process without
running the whole process down, or wanting to make the measurement at a more convenient
location.
It is important to keep in mind that changing the pressure of a gas changes the dew point
temperature of the gas. If the sensor is at a dierent pressure than the process itself, there may
be an error of several tens of degrees in the dew point measurement.
Chapter 4 – Installation
27
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