Non-contact measurement of speed and length for limited space

When space is limited.
With the VLM502 the ASTECH Company provides a contactless working gauge, especially designed for application with limited space. The VLM502 bases on the successful VLM500 series. Compared to the VLM500 the internal components were separated and put into two smaller housings. In the compactly structured gauge head (VLM502- O) the primary sensor and the illumination unit are covered. The subsequent data processing and data output is done in the evaluation unit (VLM502- E). In addition with the adaption of the receiving optics the size of the housing for the gauge head could be reduced significantly.
The VLM502 measures lengths and velocities without contact independently from the material and due to its comprehensive interfaces it can easily be integrated into automation and quality assurance processes in different industrial sectors.


The VLM502 works optically and contact-free. Based on a CCD sensor it implements the spatial filter principle. Spatial filter is the generic term for a measuring principle for the optical determination of velocity and length of moving objects.

The spatial filter is based on the filtering effect of lattice-like structures (grid modulation). Basically, the functional principle of the VLM502 can be described as follows: The illuminated measuring object is projected through lenses on the CCD sensor which acts as an optical grid. The VLM502 is equipped with a LED light source for the illumination. Due to the grid modulation a signal frequency, which is proportional to the speed, occurs upon movement of the object. The device calculates the velocity from the measured signal frequency. Several control circuits loops for an automatic adjustment to most diverse materials.

There are rarely requirements on the surface character of the measuring object. Precise measurements are facilitated on periodic structures as well as on stochastic surfaces of metals, wood, rubber or paper.


  • Contactless
  • Measuring range up to 50 m/s
  • Measuring uncertainty ±0.025 %
  • Working distance: 85 mm
  • Slip-free
  • Wear-free
  • Material independent
  • High power illumination LED
  • No dangerous laser radiation
  • Robust and precise
  • Insensitive to contamination
  • Economical
  • Various interfaces
  • Easy installation
  • Easy maintenance
  • PC software for parameterization
  • 60-months warranty
  • Quality product made in Germany


Robust and precise
The robust and small construction of the VLM502 facilitates its use in harsh and space limited industrial environments and allows slip-free measurements of speed and length in a wide range of production processes while achieving a high measuring dynamic and accuracy.

Low maintenance
Due to the contact-free measuring principle the VLM502 does not only work more precisely than other systems that are subject to slip, but also without wear through friction. This minimizes the need for servicing. Damage or impurity of the surface to be measured does not occur.

Flexible and versatile
The VLM502 works autonomously. Sensor, illumination, signal processing and power supply have been integrated into the two housings. The comprehensive parameterization provides the user with a wide range of functionalities which ensure flexible operation. For example the acquisition and output times, sliding averaging or scaling of speed and length outputs can be parameterized. All devices are bus compatible (RS232, RS422/RS485, USB, Profibus, Profinet, Ethernet) and can be synchronized. Via its versatile interfaces the VLM502 can easily be integrated into existing processes, controls or into process data acquisition systems. It can be set up and be parameterized easily. The user software "VLMTool" is provided for free.

Quality product
The high quality standard of the VLM502 is expressed by a considerably long period of warranty which is 60 months.

Standard scope of delivery as a set
Due to the complete scope of delivery the VLM502 is quickly applicable:
  • Measuring device VLM502
  • Programming interface according to customer specification
  • Printed manual in English or German
  • USB memory stick with documentation in English and German and user software VLMTool (for Microsoft® Windows)
  • power supply cable, connection cable
  • connection cable between gauge head and evaluation unit
  • Alignment tool for the working distance
  • Parameter list and wiring plan

Selectable interfaces
A wide range of applications can be covered with selectable interfaces or the signal in- and outputs:

  • Up to two programming interfaces (RS232, USB, RS422/485)
  • Pulse output with two phases A and B (resolution 8 ns):
    • IPPL (12 V ... 24 V passive, max. 25 kHz)
    • IP5V (5 V active, max. 4 MHz)
    • IPPP (24 V active, max. 4 MHz)
  • In- and outputs (IOPL):
    • ERROR output (extensive self-diagnosis of the device)
    • STATUS output (programmable)
    • TRIGGER 1 input
    • STANDBY / TRIGGER 2 input
    • DIRECTION input
  • PROFIBUS DP connection
  • Ethernet connection
  • Profinet connection
  • Analogue output cards:
    • IA00 (0 mA ... 20 mA)
    • IA40 (4 mA ... 20 mA)
    • IA04 (0 mA ... 24 mA)

Powerful options and accessories
Several options and accessories provide more possible applications and benefits when using the VLM502:

  • Automatic direction detection
  • LBC - Light barrier controller (to connect up to 8 light barriers)
  • ACM - Pointer instrument to display signal quality or velocity
  • PAXICA - Counter/Display
  • Mounting plates
  • Linear alignment units
  • Protective and cooler case

Technical data

Nominal distance 85 mm
Working range max. ±15 mm
Measuring range 0.6 ... 3000 m/min
Measuring uncertainty1) < 0.025 % in nominal distance
Reproducibility1) < 0.025 %
Averaging-/Update-Time > 0.2 ms with additional 1 ... 32 times sliding average
Length measuring range Internal length range up to 2,000,000 km
Detector / principle CCD sensor / spatial filter with semiconductor grid as reference
Illumination White light LED (expected life span: > 5 years 2))
State indicator
(VLM502 - E)
Sginal (green), Error signal (red), Communication (yellow), Forward (Green), Backward (green)
Power supply, consumption 24 VDC
max. 25 W
Temperature range 0 °C ... 50 °C
Protection class IP 65
EMC Industrial standard in compliance with CE
Weight, Housing dimensions VLM502 - O: approx. 1,7 kg, 135 mm x 140 mm x 67 mm (without connections)
VLM502 - E: approx. 2,2 kg, 140 mm x 140 mm x 91 mm (without connections)
Programming interface
(max. 2)
for parameter setting, data output and firmware update:
USB (IUSB), RS-232 (I232), RS-422/RS-485 (I4UN), isolated
Opto-isolated outputs3) 2x (Error, Signal status)
Opto-isolated inputs4) 3x (External trigger signal, Idle mode / Lock5),
Definition of the direction of the movement
Pulse output (Encoder) A/B, 2 phases 90°, Resolution 8 ns, 0.2 Hz ... 25 kHz
Optionally as Open Collector (IPPL), 5V TTL (IP5V)6)
or Push Pull (IPPP) 6)
Analog output Current output, adjustable as 0 ... 20 mA, 0 ... 24mA, 4 ... 20 mA (IAUN)
Fieldbus interface Profibus DP (IFBP), Telnet via FastEthernet (IFFE), Profinet IO (IFPN)
Standard scope of delivery VLM500, Programming interface on customer request, Power supply cable, Connection cable, connection cable between gauge head and evaluation unitpositioning aid, USB memory stick with documentation and software, printed manual

1 DIN 1319 / ISO 3534, of measured length, test conditions: measuring length 10 m, active tracking, constant conditions in: temperature (20 °C), distance, velocity, illumination
2 Simple replacement by user.
3 OpenCollector interface card (IOPL). Connections are isolated and short circuit proof.
4 Opto-isolated, short circuit proof, max. voltage 50 VDC, 36 VAC.
5 The idle mode input can be used as a second trigger input.
6 IP5V and IPPP provide output frequencies up to 4 MHz.


Mr. Jörg Boddien

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