OpenDRO User's Guide

6 Scales

OpenDRO supports both Chinese and quadrature scales.

6.1 Chinese Scales

Chinese scales refer to any of a large number of linear scales and calipers that are sourced from China and based on capacitive sensing technology originally developed by Sylvac.  These scales come in a huge variety of lengths and styles.  Chinese scales usually have a four-pin output port on the side of the scale that sends the scale position data to the DRO.  There are four different protocols used for sending this data:

  • 24BIT - Two 24-bit, binary numbers are sent with the first representing the absolute position and the second representing the relative position.  The two numbers are counts with a resolution of 20480 counts per inch.
  • 21BIT - A single 21-bit, binary number is sent representing the absolute position.  The number has a resolution of 2560 counts per inch.  The 21BIT scales differ in that the DRO must provide a clock to read out the data rather than the scale providing the clock like other Chinese scale types.  See the 21 bit protocol information at the ShumaTech web site for information on how to connect a 21 bit protocol scale.
  • BIN6 - A single 20-bit, binary number followed by a 4-bit flag field.  The 20-bit number is the count with a resolution of 2540 counts per inch when the scale is in metric mode.
  • BCD7 - A single 24-bit, BCD number followed by a 4-bit flag field.  The BCD number represents the seven digits shown on the scale display.

In addition, the 24BIT and BCD7 scales support a "fast" mode where they send the data to the DRO at a much higher rate than normal.  The 21BIT and BIN6 scales do not support that feature.

The metal backs of Chinese scales are connected to one of the battery terminals.  For 24BIT and BCD7 scales, the metal backs are connected to the positive battery terminal.  For 21BIT and BIN6 scales, the scale beams are connected to the negative battery terminal.   If you mix both types on one DRO, then you must insulate them to avoid shorting the DRO power supply through the machine.

WARNING!!! Do not mix 21BIT or BIN6 scales with 24BIT or BCD7 scales without electrically isolating one scale type or the other.

Except for iGaging-branded 21BIT scales, it is difficult to determine which protocol a Chinese scale uses just by looking at it.  You can differentiate between BIN6 and a 24BIT/BCD7 by using a multimeter to determine which side of the battery the scale back is connected to.  Differentiating a BCD7 from a 24BIT is more difficult and is best done with an oscilloscope.  Note, however, that 24BIT scales are much more common than BCD7 scales.  Most of the time, you can set the scale type to "Auto" and OpenDRO will automatically detect and configure the scale type.

6.2 Quadrature Scales

Quadrature scales are linear or rotary encoders that output two signals that are 90 degrees out of phase with each other and includes most glass scales encountered on machining equipment.  OpenDRO supports any quadrature encoder that outputs a signal that is electrically compatible with the hardware it is running on.  The DPU/DRO-550 supports quadrature encoders that output a digital, 5V output.  A partial list of scale manufactures and their compatibility with the DPU/DRO-550 is shown in the following table.

Manufacturer Support
Acu-rite Some models
Anilam Yes
Ditron Yes
DRO Pros Yes
Easson Yes
Futaba No
Heidenhain Some models
Jenix Yes
Meister Yes
Mitutoyo Some models
mTech Yes
Newall Some models
RSF Some models
Sargon Yes
Sino Yes
Sinpo Yes
Sokki No
Sony No
Teledyne Gurley No
Uniq Yes
US Digital Yes