Basic function principles

Properties

The KL320x analog input terminals enable resistance sensors to be connected directly. A micro-controller within the terminal is used for converting and linearizing the resistance to a temperature value. The temperatures are displayed as follows:

In addition to this, a broken wire or short circuit is reported to the Bus Coupler or to the controller, and indicated by the ERROR LED.

PT100, NI100, PT200, PT500, NI120, NI1000 and PT1000 as well as NTC10K of the KL3204-0030 elements are implemented over their full measuring ranges as resistance sensors. The terminal can be fully configured over a fieldbus. A self-defined scaling of the output can, for instance, be performed, or the temperature conversion can be switched off. In the latter case, the measurement is output in the range from 10 Ω up to 1.2 kΩ with a resolution of 1/16 Ω (the internal resolution of the resistance value is 1/255 Ω).

Process data output format

In the delivery state, the measured value is displayed in increments of 1/10° C in two's complement format (integer). The complete measuring range is output for each resistance sensor. Other display types can be selected via the feature register (e.g. sign/amount representation, Siemens output format).

Measured value

Hexadecimal output

Signed integer output

-250.0°C

0xF63C

-2500

-200.0°C

0xF830

-2000

-100.0°C

0xFC18

-1000

-0.1°C

0xFFFF

-1

0.0°C

0x0000

0

0.1°C

0x0001

1

100.0°C

0x03E8

1000

200.0°C

0x07D0

2000

500.0°C

0x1388

5000

850.0°C

0x2134

8500

Resistance limit values

The linearization of the characteristic curve is continued with the coefficients of the upper range limit up to the limit stop of the A/D converter (approx. 500 Ω for PT100).

The smallest negative number is displayed (0x8001 corresponds to -32767).
For over range or under range the red error LED is switched on.

Process data

The process data that are transferred to the terminal bus are calculated using the following equations:

Variable

Meaning

X_RL

ADC value of the supply cables

X_RTD

ADC value of the temperature sensor, including one supply cable

X_R

ADC value of the temperature sensor

A_a, B_a

Manufacturer gain and offset calibration (R17, R18)

A_h, B_h

Manufacturer scaling

A_w, B_w:

User scaling

Y_R

Temperature sensor resistance value

Y_T

measured temperature in 1/16 °C

Y_THS

Temperature after manufacturer scaling (1/10 °C)

Y_TAS

Temperature after user scaling

Y_AUS

Process data to PLC

a) Calculation of the resistance value:

X_R = X_RTD-X_RL (1.0)

Y_R = A_a * (X_R - B_a) (1.1)

b) Curve linearization:

Y_T = a1 * Y_R2 + b1* Y_R + c1 (1.2)

or

Y_T = Y_R if output in Ω (1.3)

c) Neither user nor manufacturer scaling are active:

Y_AUS = Y_T (1.4)

d) Manufacturer scaling active (factory setting):

Y_THS = A_h * Y_T + B_h (1.5)

Y_AUS = Y_THS

e) User scaling active:

Y_TAS = A_w * Y_T + B_w (1.6)

Y_AUS = Y_TAS

f) Manufacturer and user scaling active: (1.7)

Y_1 = A_h * Y_T + B_h

Y_2 = A_w * Y_1 + B_w

Y_AUS = Y_2

Basic function principles 1:
Data flow of the KL320x