Alpes Lasers . TC-3 Manual do Utilizador descarregar pdf (Página 24)

Page 24 · TC-3 Temperature Controller User’s Manual

required temperature range. The typical setting is 100μA, but your

application will determine the actual needs.

The Steinhart-Hart Equation

As can be seen from the temperature versus resistance graph above,

resistance varies inversely with temperature in a non-linear fashion.

This relationship can be accurately modeled by polynomial equations,

and one such being the Steinhart-Hart equation:

=A+B *ln ( R )+C *ln ( R)

The coefficients A, B, and C can usually be obtained from the

thermistor manufacturer. The TC-3 defaults to the coefficients for the

BetaTHERM 10K3A1 thermistor (A = 1.12924x10

-3

, B = 2.34108x10

-4

, C

= 0.87755x10

-7

). You can change the coefficients under the Sensor

Coeffs menu.

Working With RTDs

Like thermistors, RTDs also function by converting temperature into

resistance, but unlike thermistors, RTDs increase in resistance as

temperature increases. RTDs are also a fairly linear device, meaning

they can be used across a much broader temperature control range.

According to IEC751, the resistance/temperature relationship is

determined using one of two equations, dependent on the temperature

or resistance value being measured. For resistances above the R

value

(resistance at 0°C, typically 100Ω) of the RTD, the following equation is

used:

R=R

(1 +AT+BT

)

Below R

, an additional term is added to the equation:

R=R

[1+AT+BT

+C (T −100 ) T

]

In both of these equations, R

is the resistance of the RTD at 0°C, and

A, B, and C are the coefficients as defined by IEC751, through

regression analysis, or by using the Callendar-van Dusen method. By

default, the TC-3 uses the Laboratory standard coefficients, which are

for a 0.003926Ω/ Ω/°C curve (A = 3.9848x10

-3

, B = -0.58700x10

-6

, C =

4.0000x10

-12

, and R

= 100).

1 2 ... 19 20 21 22 23 24 25 26 27 28 29 ... 40 41

Comentários a estes Manuais

Sem comentários

Alpes Lasers . TC-3 Manual do Utilizador Página 24

Comentários a estes Manuais