Keithley 3721-ST User Manual

Section 4: Basic DMM operation Series 3700A System Switch/Multimeter Reference Manual
4-24 3700AS-901-01 Rev. D/June 2018
Autodelay and autorange settings
For the standard RTD values (PT100, D100, F100, PT385, and PT3916), use 1 kΩ. For user-set
RTDs, use 1 kΩ or 10 kΩ, depending on the alpha, beta, delta, and R
0
values.
For thermocouples, the autodelay function is 1 ms when switching between measurements.
For thermistors, for:
• 2252 Ω and 5 kΩ: 100 Ω to 10 kΩ, dependent on temperature
• 10 kΩ: 1 kΩ to 10 kΩ, dependent on temperature
Thermocouples
For thermocouples, temperature measurement range depends on which type of thermocouple is
being used. Thermocouple types J, K, N, T, E, R, S, and B are supported.
Type
Range
Resolution
J
-200 °C to +760 °C
0.001 °C
K
-200 °C to +1372 °C
0.001 °C
N
-200 °C to +1300 °C
0.001 °C
T
-200 °C to +400 °C
0.001 °C
E
-150 °C to +1000 °C
0.001 °C
R
0 °C to +1768 °C
0.1 °C
S
0 °C to +1786 °C
0.1 °C
B
+350 °C to +1820 °C
0.1 °C
When two wires made up of dissimilar metals are joined together, a voltage is generated. The
generated voltage is a function of temperature. As temperature changes, the voltage changes. The
thermocouple voltage equates to a temperature reading. This is the basic operation principle of the
thermocouple.
When you connect a thermocouple directly to the input of the Series 3700A, at least one of those
connections will be a junction made up of two dissimilar metals. Hence, another voltage is introduced
and is algebraically added to the thermocouple voltage. The result will be an erroneous temperature
measurement.
To cancel the affects of the unwanted thermal voltage, the thermocouple circuit requires a reference
junction that is at a known temperature.
The Series 3700A has an open thermocouple detection circuit. Long lengths of thermocouple wire
can have a large amount of capacitance, which is seen at the input of the DMM. If an intermittent
open occurs in the thermocouple circuit, the capacitance can cause an erroneous on-scale reading.
The open thermocouple detection circuit, when enabled, applies a 100 µA pulse of current to the
thermocouple before the start of each temperature measurement. For more detail, see Open
thermocouple detection (on page 8-18).
The default setting is for open thermocouple detection to be on (dmm.opendetector = dmm.ON).
For information about temperature equations, see Temperature equations (on page 4-33).

Keithley 3721-ST Specifications

General

Brand	Keithley
Model	3721-ST
Category	Multimeter
Language	English