1–2 Getting Started
1.1 Introduction to the Instrument
The SIM923A RTD Temperature Monitor provides excitation and
readout for a single resistive temperature detector (RTD). Analog
outputs, both proportional to temperature and the buffered sensor
voltage, are available on the front panel.
1.1.1 Overview
The SIM923A uses a ratiometric design, where the excitation current
is passed through both an internal, stable reference resistor and the
user’s resistive thermometer. The instrument measures the ratio
of the voltage across the user’s resistor to the voltage across the
reference resistor, multiplied by the (known) value of the reference
resistor, to obtain the user result.
Two separate excitation and reference circuits are included in the
SIM923A, a 1 mA excitation appropriate for ∼1 kΩfull-scale mea-
surements, and a 10 µA excitation useable for up to ∼100 kΩfull-
scale measurements. The excitation is also reversable, permitting the
user to test for potential offset voltages in the setup.
A precision 24–bit analog-to-digital converter records the results.
New sensor measurements are available at a rate of 5 conversions
per second.
1.2 Front-Panel Operation
The front panel of the SIM923A(see Figure 1.1) provides a simple
operator interface.
1.2.1 Excitation
The current source of the SIM923A RTD Temperature Monitor can
be fully controlled from the front panel.
To select between 10 µA and 1 mA briefly tap [Excitation]. To toggle
the current on and off,hold [Excitation] for about 1 second, until the
display switches between the numerical result and the word .
The excitation can also be controlled with the EXCIand EXONremote
interface commands.
1.2.2 Units
The SIM923A displays results either as raw sensor units (in ohms) or
temperature (in kelvin). Pressing [Units] toggles between these two
modes; the active units are indicated by the illuminated K, or Ω(or
SIM923A RTD Temperature Monitor
