Power supply requirements, Sampling from a process – Vaisala DMT132 User Manual
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USER'S GUIDE____________________________________________________________________
24 __________________________________________________________________ M211289EN-A
Power Supply Requirements
The DMT132 transmitters are designed to operate with a supply voltage
of 10 ... 28 VDC. The allowed voltage range depends on the loop
resistance (R
L
):
- For
R
L
0 ... 100 Ω, supply voltage range is 10 ... 20 VDC.
- For
R
L
0 ... 500 Ω, supply voltage range is 20 ... 28 VDC.
NOTE
Maximum allowed R
L
is 600 Ω, as long as the following equation
applies:
V
R
U
L
5
.
7
40
min
When R
L
= 600 Ω, supply voltage range is 22.5 ... 28 VDC.
NOTE
The DMT132 can be powered by the MI70 indicator or the USB service
cable. You can plug in the MI70 indicator or the USB service cable while
the transmitter is powered from connector I.
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 dewpoint temperature of the gas. If the sensor is at a
different pressure than the process itself, there may be an error of several
tens of degrees in the dewpoint measurement.
Make sure there is sufficient flow of gas to the sensor (for example,
1 l/min) to give a representative sample.
You can use the Vaisala Humidity Calculator to simulate the effect of
pressure change to dewpoint. The Humidity Calculator can be found at: