Agilent 34980A Multifunction Switch/Measure Unit *34980-90005*
Agilent 34980A Multifunction Switch/Measure Unit *34980-90005*
Agilent 34980A Multifunction Switch/Measure Unit *34980-90005*
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Thermocouple <strong>Measure</strong>ments<br />
Features and Functions 3<br />
The instrument supports the following thermocouple types: B, E, J, K, N,<br />
R, S, and T using ITS- 90 software conversions. The default is a J- Type<br />
thermocouple.<br />
Thermocouple measurements require a reference junction temperature.<br />
For the reference junction temperature, you can use an internal<br />
measurement on the module (34921A only), an external thermistor <br />
or RTD measurement, or a known fixed junction temperature.<br />
The internal reference junction source is valid only on channels 1<br />
through 40 on the 34921A with the 34921T terminal block installed.<br />
If you select an external reference, the instrument makes<br />
thermocouple measurements relative to a previously- stored RTD or<br />
thermistor measurement stored in a reference register. To store a<br />
reference temperature, first configure a multiplexer channel for an<br />
RTD or thermistor measurement. Then assign the measurement <br />
from that channel as the external reference. When you initiate a<br />
measurement on an external reference channel, the acquired<br />
temperature is stored in volatile memory in the reference register.<br />
Subsequent thermocouple measurements use the stored temperature<br />
as their reference. The temperature remains in memory until you<br />
measure a subsequent external reference value in the reference<br />
register or remove the mainframe power.<br />
If you select a fixed reference temperature, specify a value between <br />
- 20 °C and +80 °C (always specify the temperature in °C regardless<br />
of the temperature units currently selected).<br />
The accuracy of the measurement is highly dependent upon the<br />
thermocouple connections and the type of reference junction used.<br />
Use a fixed temperature reference for the highest accuracy<br />
measurements (you must maintain the known junction temperature).<br />
The internal isothermal block reference (34921A only) requires no<br />
external wiring but provides lower accuracy measurements than a fixed<br />
reference.<br />
The thermocouple check feature allows you to verify that your<br />
thermocouples are properly connected for measurements. If you enable<br />
this feature, the instrument measures the channel resistance after <br />
each thermocouple measurement to ensure a proper connection. If an<br />
open connection is detected (greater than 5 k on the 10 k range),<br />
the instrument reports an overload condition for that channel <br />
(or displays “OPEN T/C” on the front panel).<br />
<strong>Agilent</strong> <strong>34980A</strong> Mainframe User’s Guide 97