Two new single-axis position display units have been introduced by Heidenhain (G.B.) Limited to cater for a wide range of applications, from the simplest single axis measurement of linear, rotary or angular displacement to the storage and evaluation of measured values and statistical functions.
Replacing the previous ND 200 series sold as standard products since 1995, the new ND 280 and ND 287 position display units have an expanded functionality. Both models make use of thin-film transistor (TFT) technology for enhanced image stability on either the monochrome or colour LCD screen, with ergonomically designed soft keys contributing to improved operation and parameter setting.
Linear error compensation and non-linear axis error compensation (200 compensation points) is standard to both the ND 280 and ND 287, as is input/output of parameter backup and compensation value lists. With the ND 287 it is also possible to write up to 10,000 measured values to an internal memory and to evaluate them statistically. These measured values can be captured via an external trigger or on a time basis, and allow the mean value and standard deviation to be calculated. If required, the histogram of the measurement can be calculated and displayed (symmetrically and asymmetrically). On completion of the measurement series, a diagram shows the corresponding curve.
In addition, it is possible to maintain control charts of the mean value, the standard deviation and the control deviation. The user has to specify the process monitoring constraints, such as number of random samples, duration of monitoring and action limits, and in this way the drift of a process can be determined and notification displayed should intervention be required.
The base model ND 280 position display unit is equipped with RS 232, USB and encoder connections, while the ND 287 has a modular design that accommodates a switching inputs/outputs function and slots for an Ethernet/Profibus module and a second encoder connection. Equipping the ND 287 with a second axis module allows data from two encoders to be combined to provide either the sum or difference of the two measurement inputs.
The Ethernet/Profibus capability of the ND 287 enables integration to a data transfer network as part of a production metrology application. However, optional analogue sensors (e.g. for temperature compensation of the measuring axis) can be connected to either model, as can encoders with Heidenhain’s EnDat 2.2 interface. This is a digital, bidirectional interface capable both of transmitting position values from incremental and absolute encoders as well as transmitting or updating information stored in the encoder or saving new information. Thanks to the serial transmission method only four signal lines are required, with data transmitted in synchronism with the clock signal from the subsequent electronics. The type of transmission (position values, parameters, diagnostics, etc,) is selected by mode commands that the subsequent electronics send to the encoder.