Campbell AVW1 Specifikace stáhnout pdf (Strana 39)

AM16/32B Relay Analog Multiplexer

If a mix of TCs and other sensor types are multiplexed through the

AM16/32B, it is generally best to locate the reference junction on the

AM16/32B, as shown in Figure 19.

AM16/32B Reference - An external reference, usually a thermistor,

can be located at the AM16/32B, as shown in Figure 19. This

approach requires an additional single-ended datalogger input to

measure the reference. Position the reference next to the COM

terminals and, when practical, measure the thermocouples on SETs

that are in close proximity to the COM terminals in order to minimize

thermal gradients.

Thermal Gradients - Thermal gradients between the AM16/32B's

sensor input terminals and COM terminals can cause errors in

thermocouple readings. For example, with type T thermocouples, a

one degree gradient between the input terminals and the COM

terminals will result in an approximate one degree measurement error.

Installing the aluminum cover plate (included with AM16/32B) helps

to minimize gradients. For best results the AM16/32B should be

shielded and insulated from all radiant and conducted thermal sources.

When an enclosure is used, gradients resulting from heat conducted

along the thermocouple wire can be minimized by coiling some wire

inside the enclosure. This technique allows heat to largely dissipate

before it reaches the terminals. If the AM16/32B is housed in a field

enclosure, the enclosure should be shielded from solar radiation.

FIGURE 20. AM16/32B Aluminum Cover Plate

6.6.2 Single-ended Thermocouple Measurement

In single-ended thermocouple measurements, the following

precautions must be taken to ensure accurate measurement:

Only shielded thermocouple wire should be used; the sensor shields

should be tied to multiplexer input shield (“

”) terminals.

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Campbell AVW1 Specifikace Strana 39