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modules or I/O modules) create a thermal gradient across the

terminals of the FP-TB-3, which you can estimate by dividing the

larger of the amounts of heat dissipated by each of the adjacent

modules by 20 W/°C (11 W/°F). For example, if the FP-TB-3 is

between an analog input module dissipating 0.35 W and a discrete

output module dissipating 3 W, the estimated thermal gradient is

3W ÷ 20 W/ °C = 0.15 °C.

Estimating Thermal Gradients across the FP-TB-1

and FP-TB-2 Terminal Bases

The lack of isothermal construction in the FP-TB-1 and FP-TB-2

terminal bases makes them more susceptible to errors caused by

thermal gradients. These terminal bases are recommended for use

with thermocouple measurements only where these errors are

acceptable or where precautions can be taken to minimize them.

(Refer to the next section, Minimizing Thermal Gradients when

Using the [c]FP-TC-120.) Adjacent FieldPoint modules (either

network modules or I/O modules) create a thermal gradient across

the terminals of the FP-TB-1, which you can estimate by dividing

the larger of the amounts of heat dissipated by each of the adjacent

modules by 1 W/°C (0.6 W/°F). For example, if the FP-TB-1/2 is

between an analog input module dissipating 0.35 W and a discrete

output module dissipating 3 W, the thermal gradient would be

3W÷ 1 W/°C = 3 °C. The typical thermal gradient created by the

FP-TC-120 mounted on an FP-TB-1 (neglecting any adjacent

modules) is about 0.2 °C.

Minimizing Thermal Gradients when Using

the [c]FP-TC-120

The most common source of thermal gradients, particularly for the

FP-TB-1 and FP-TB-2, is the heat generated by adjacent modules.

For example, placing an FP-TB-1 next to an FP-1000 network

module can create more than a 1 °C thermal gradient. You can

avoid such a high thermal gradient by mounting a lower-power

module or the FieldPoint Bus Extender Cable (part number

185576-15) between the FP-TC-120 and any higher-power

modules in the system. This precaution is generally not necessary

if you use the FP-TB-3.

Hot or cold air draft can be another source of thermal gradients.

However, circulating air around nearby components may help them

dissipate heat and reduce thermal gradients on the terminal base.

National Instruments CFP-TC-120 User Manual

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