Vaisala HUMICAP DMT132, User Manual

Page: 23 / 72

Maximum allowed R
L
is 600 Ω, as long as the following equation applies:
�
min
=
�
�
40 + 7 . 5 ∨
When R
L
= 600 Ω, supply voltage range is 22.5 ... 28 VDC.
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.
3.4 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.
Keep in mind that changing the pressure of a gas changes the dew point 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 dew point 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
dew point. The Humidity Calculator is available at:
www.vaisala.com/humiditycalculator .
3.5 Sampling Accessories for DMT132
3.5.1 DMT242SC Sampling Cell
The DMT242SC is a basic sampling cell with only the main sampling cell body. The inlet and
outlet are female threaded sample connectors (inlet G3/8", outlet G1/4" ISO). See
Figure 16
(page 22) .
The DMT242SC is suitable for users requiring only a sampling cell to fit the transmitter into
and doing further assembly (piping into inlet and outlet, valves, possible flow meter) by
themselves.
Chapter 3 – Installation
21