NDC BETA LaserMike LaserSpeed Pro 8500-4, Инструкция по эксплуатации, Страница: 58 / 348

4-10 LaserSpeed Pro 8500-4 Instruction Handbook: Interfacing with the LS8500-4
4.2.1.9 Pulse Output Delay
The pulse output uses a DDS circuit to generate the pulse output. The speed of the product being measured
is obtained by measuring the speed of the product up to 20,000 times per second. This measurement rate is
higher than any process control device can handle. Therefore, the measurements are gathered in 2ms incre-
ments and averaged together to provide a speed measurement every 2ms. The speed measurements are
sent to the digital output and to the DDS to update the pulse generator with new speed data every 2ms. For
most cases, a 2ms response time is too fast for most process controllers. Process controllers are used to tak-
ing the speed information from a mechanical encoder. The mechanical encoder has a certain amount of me-
chanical inertia that mechanically slows down the response to fast speed changes or smooths out any fast
changes in the speed of the product. Since the LaserSpeed gauge makes its measurement via an optical
measurement, there is no mechanical smoothing of the speed information.
Electronic smoothing of the speed measurements have been added to the digital data in order to simulate the
mechanical smoothing of the mechanical encoder. The mechanical inertia and the electronic smoothing of
the data introduce a delay in the data as well as the smoothing of the data. For the LaserSpeed gauge the
delay is equal to ½ the smoothing amount. For encoders the delay is determined by the amount of mechani-
cal mass of the encoder wheel or roller.
The LaserSpeed gauge implements a forward running average to achieve data smoothing. The forward run-
ning average is depicted by the following formula:
S
DIP
= 1/nΣ
1
-n
S
n
Where:
S
DIP
=Average speed (smoothed speed)
n = the number of Speed measurements used in the average ( DIP )
S = Individual Speed measurements from the 2ms average