Advantech iDAQ-815, User Manual

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iDAQ-815 User Manual 14
Figure 3.4 Start and stop of the analog input acquisition with delay.
Buffered analog input acquisition has several advantages over instant analog input
acquisition:

The start and stop time of acquisition (or duration of the acquisition) can be pre -
cisely controlled by hardware trigger signals.

The ADC conversion rate is configurable and the sample rate can be much
higher by using hardware sample clock signals.

Time between samples is deterministic.
3.2.3 Analog Input Isolation
The analog input circuitry is equipped with a galvanic isolator, which can withstand a
large continuous voltage between external side and internal side. This prevents the
internal components and the host devices (e.g. PC) from damaging when such fault
condition happens.
3.3 RTD Properties
3.3.1 RTD Type
There are many RTD types made by different materials, such as platinum (Pt), nickel
(Ni), copper (Cu), and nickel-ferrite alloy (NiFe). Each type of RTD has different tem -
perature sensitivity, which is the percentage of resistance change over unit tempera -
ture, and measurable temperature range.
RTD is usually named after the material made with and the resistance value at 0 °C.
For example, a Pt100 RTD is made with platinum and has 100 Ω of resistance at 0
°C; a NiFe604 RTD is made with nickel-ferrite alloy and has 604 Ω of resistance at 0
°C.
RTD sensitivity changes a little over temperature. That means the resistance-tem
-
perature relationship is not linear. However, it is usually represented by a tempera -
ture coefficient α as the difference of the resistance at 100 °C and 0 °C, divided by
the resistance at 0 °C multiplied with 100 °C.
For example, a Pt100 (385) RTD has a resistance of 100 Ω at 0 °C and 138.51 Ω at
100 °C. The temperature coefficient can be calculated by the following equation.