Agilent Technologies U2802A manual

Features and Functions 2

Figure 2-6Ground-referenced and differential signal sources configuration in U2802A

Zero mode: In zero mode, the positive and negative inputs of the instrumentation amplifier are shorted together. The output of the instrumentation amplifier is driven out to the corresponding AI channel. The voltage measured in this mode corresponds to the offset voltage of the channel. This voltage can be subtracted out of the subsequent thermocouple mode measurements in order to increase the measurement accuracy. Do take note that this mode only works for channels that have been configured to be in the thermocouple mode. Channels configured for bypass mode will not be affected when this mode is selected.

Each channel is equipped with an open thermocouple detection feature, where the 10 MΩ resistor is tied to the +15 V power supply rail. This feature can only be globally enabled or disabled for all channels, regardless of the channel mode setting. When enabled, outputs of the channels are set to thermocouple mode where the inputs are left open- circuited. This causes the positive power supply rail voltage (above +10 V) to be saturated up, indicating that the channel either has a broken thermocouple or the thermocouple is not connected. For channels set to bypass mode, channels with an open- circuited input will also be saturated to the positive supply rail voltage.

Agilent U2802A 31-Channel Thermocouple Input User’s Guide 33