|BECKHOFF KL3132, KL3142, KL3152, KL3162, KL3172, KL3182: Product Overview|
The accurate analog input terminals can be used to measure two voltages (KL3132, KL3162, KL3172, KL3182) or two currents (KL3142, KL3152), and to display them with a resolution of 16 bit (65535 steps). High-precision measurements are ensured by cyclic self-calibration.
By default, the inputs are switched as differential inputs. For the terminals terminals KL3132, KL3162, KL3172 and KL3182, the terminal point -E1 of channel 1 can be switched to internal analog ground with bit R32.6 of the feature register.
Analog values are represented as follows:
|0 V||0 V||0 mA||4 mA||0||0x0000|
|10 V||2 V||20 mA||20 mA||65535||0xFFFF|
|-10 V||-2 V||-32768||0x8000|
|+10 V||+2 V||+32767||0x7FFF|
The terminal continuously takes measurement readings and stores the raw values of its A/D converter in register R0 (RAM). After each recording of the analog signal, a correction is calculated using the compensation and, if necessary, calibration values. This is followed by manufacturer and user scaling:
|YA = (XADC + BA) x AA||(1.0)||Manufacturer compensation (if calibration inactive)|
|YA = ((XADC + BK) x AA) x (AGK / AK)||(1.1)||Manufacturer compensation / calibration (if calibration activated)|
|YH = YA x AH + BH||(1.2)||Manufacturer scaling|
|Yaus = YH x AW + BW||(1.3)||User scaling|
|XADC||Output value of the A/D converter||||-|
|Yaus||Process data for controller||||-|
|BA||Offset of the manufacturer compensation (can be deactivated via bit R32.5 of the feature register)||||R17|
|AA||Gain of the manufacturer compensation (always active)||||R18|
|BK||Calibration offset (can be activated via bit R32.5 of the feature register)||||R1|
|AK||Calibration gain (can be activated via bit R32.5 of the feature register)||||R2|
|AGK||Gain of the basic calibration (can be activated via bit R32.5 of the feature register)||||R23|
|BH||Offset of the manufacturer's scaling (can be activated via bit R32.1 of the feature register)||||R19|
|AH||Gain of the manufacturer's scaling (can be activated via bit R32.1 of the feature register)||[1 x 2-16 + 1]||R20|
|BW||Offset of the user's scaling (can be activated via bit R32.0 of the feature register)||||R33|
|AW||Gain of the user's scaling (can be activated via bit R32.0 of the feature register)||[1 x 2-8 + 1]||R34|
The analog channels are calibrated periodically. Analog switches are provided for this purpose, so that the various calibration signals can be connected. It is important for this process that the entire signal path, including all passive components, is examined at every phase of the calibration. Only the interference suppression elements (L/C combination) and the analog switches themselves cannot be examined.
The calibration interval is set in register R40 in steps of 100 ms. During calibration, no current process data are present. Value 0 is present. The terminal indicates active calibration by setting bit SB1.6 in the status byte, and by switching off the associated RUN LED. Calibration can be disabled by the controller via control byte CB1.1 if necessary. If calibration is disabled over a prolonged period, the terminal carries out a forced calibration, in order to compensate any voltage drifts that may be caused by changes in temperature. The forced calibration interval is specified via register R44 as a multiple of the calibration interval. If a further calibration between two cycles is required, this can be started manually by setting bit CB1.0. The terminal then acts as if it had triggered a calibration itself.
The functionality of the calibration including all features invariably refers to both channels simultaneously! The channels cannot be calibrated individually. For this reason, the registers R40, R44, R47 and R48 are only implemented once for both channels.
- In the first phase of the calibration, an input voltage of 0 V is applied to both analog inputs (zero calibration). The zero points of both analog input stages can be determined in this way. For this measurement, the respective absolute value of the channels is of interest. The value is subsequently stored in the RAM (register R1).
- During the second calibration phase, an internal reference voltage of approx. 1,8 V (final calibration) is applied to both analog inputs. In this case, it is no longer the absolute value of the measurement result that is of interest, but only any deviation from the basic calibration value determined during production (register R23). The ratio between the two values is calculated and used in the next correction calculation. The value is subsequently stored in the RAM (register R2).
During the calibration, a stabilization of the offset and gain values is carried out. The calibration values are only accepted once a certain number (specified via register R47) of measured values is inside a certain tolerance range (specified via register R48). This further increases the precision. This function can be deactivated via bit R32.7 .
The terminal offers the option of monitoring two thresholds per channel. Threshold 1 can be specified via register R35, and threshold 2 via register R36. They are activated via bits in the feature registers R32.9 and R32.10. The status of the current process data value is indicated to the controller via the status byte SB1. Possible states are: Process data equal threshold (3), process data less than threshold (2), process data greater than threshold (1).
The terminal indicates any violation of the measuring range to the higher-level controller via the status byte.
- If the current measured value is greater than 0xFFFF respectively 0x7FFF, bit SB1.1 is set.
- If it is less than 0 respectively 0x8000, bit SB1.0 is set.
In both cases, the ERROR LED of the respective channel will be on. This function can be deactivated via bit R32.8.