Campbell AM25T, Руководство по эксплуатации продукта

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AM25T Solid-State Thermocouple Multiplexer
8
TABLE 7-1. AM25T to Data Logger Wiring
Function AM25T Data Logger
12 Vdc Power 12V 12V
Power Ground G G
Analog Ground 1
⏚ ⏚
Clock CLK U or Control Terminal
Reset RES U or Control Terminal
PRT Excitation VX VX , U , or Control Terminal
Common High HI Diff H , U , or Control Terminal
Common Low LO Diff L , U , or Control Terminal
1
Analog Ground is the ⏚ terminal located between the VX and HI terminals on the
AM25T.
7.3 Sensor to AM25T Wiring
This section and the examples describe differential voltage measurements of
thermocouples. It is possible to make single-ended measurements with the
AM25T; however, they are more likely to have problems.
Shield wires are connected to the analog ground (
⏚ )
terminal next to the
measurement channel and left unattached at the sensor.
7.3.1 Thermocouple Measurement
An internal reference PRT is located in the AM25T. This reference temperature
does not require an additional data logger input to measure the reference.
Thermal gradients between the AM25T sensor input terminals and the PRT
cause errors in thermocouple readings. For example, a one-degree gradient
between input terminals and the PRT will result in a one-degree measurement
error. The thermal bar in the AM25T, which includes the strain relief, and the
AM25T cover are designed to reduce gradients. The PRT is attached to the
thermal bar.
Heat conduction along the thermocouple wire, into the terminal strips, can be
reduced by coiling excess wire inside the enclosure.
For a differential voltage measurement of a thermocouple, wire the high side of
the thermocouple to the high side of a differential input channel on the AM25T
and the low side of the thermocouple to the low side of the channel.
Thermocouples that follow the U.S. industry standards use red insulation on
the low side of the thermocouple. Wire one thermocouple per differential input
channel (FIGURE 7-2 ).