MCP960X datasheet(35/57 Pages) MICROCHIP

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DS20005426G-page 35

MCP960X/L0X/RL0X

5.2.2

THERMOCOUPLE SENSOR

CONFIGURATION REGISTER

The

MCP960X/L0X/RL0X

Sensor

Configuration

types and to select the digital filter options. This device

supports eight thermocouple types. Each type has a

unique set of error correction coefficients that are

derived from the NIST Thermocouple EMF Voltage

Conversion database.

In addition, this device integrates a first order. recursive

Infinite Impulse Response (IIR) filter, also known as

Exponential Moving Average (EMA). The filter uses the

current new temperature sample and the previous filter

output to calculate the next filter output. It also adds more

weight to the current temperature data, allowing a faster

filter response to the immediate change in temperature.

This feature can be used to filter out fast thermal

transients or thermal instability at the thermocouple

hot-junction temperature. Writing this register resets the

filter.

The filter equation is shown in Equation 5-4 and the

Filter Coefficient n is user-selectable, from Level 0 to 7.

A coefficient of 0 disables the filter function and a 7

coefficient provides a maximum digital filter. Figure 5-6

shows the filter response to a step function, which can

be used to extrapolate the filter performance to various

temperature changes.

EQUATION 5-4:

DIGITAL FILTER

FIGURE 5-6:

Filter Step Response.

Yk X



–

 Y

–



Where:

Y = New filtered temperature in TΔ

X = Current, unfiltered hot-junction

temperatures

Y-1 =Previous filtered temperature

n = User-selectable filter coefficient

k2 2





0.0

0.5

1.0

0.0

32.0

64.0

96.0

128.0

Number of Temperature Samples

n=0

n=1

n=2

n=3

n=4

n=5

n=6

n=7

SENSOR CONFIGURATION REGISTER

U-0

R/W-0

U-0

R/W-0

—

Thermocouple Type Select, Type K, J, T, N, S, E, B, R

—

Filter Coefficients

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7

Unimplemented: Read as ‘0’

bit 6-4

Thermocouple Type: Thermocouple Type Select bits

000 = Type K

001 = Type J

010 = Type T

011 = Type N

100 = Type S

101 = Type E

110 = Type B

111 = Type R

bit 3

Unimplemented: Read as ‘0’

bit 2-0

Filter Coefficient – n: Filter Coefficient bits

000 = n = 0: Filter off

001 = n = 1: Minimum filter

010 = n = 2

011 = n = 3

100 = n = 4: Mid filter

101 = n = 5

110 = n = 6

111 = n = 7: Maximum filter

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