Src-perl-lab-scale

laboratory scale logger

Software was developed to interface a Denver Instruments lab scale, model PK-6, to a computer in order to automatically record mass measurements made by the scale during long term experiments.

Currently, work is underway to adapt this software to support another scale, one in the O'Haus (Ohaus?) Navigator line. Both scales are equipped with an RS232 port, but differ in wiring and firmware.

In this wiki page I want to try to describe the workings of the older and new software under development. The new version will hopefully improve on the older, and should be a bit more generalized and configurable, though far from fully featured.

scope of work

The need for our users that is addressed by this software is to simply record measurements on some interval, which may range from seconds to hours. Where their experiment may run for days or weeks, hopefully this will free them from the need to come down to the lab to press manually read the scale.

Thus, the primary task tackled by the software is to issue the "print" command to the scale. This happens to be the letter "p" (or "P") in both cases, but other details vary -- one handles the command as an "escape", so expects the escape character followed by "p", while the other is looking for "p" followed by a carriage return.

Both scales emit a similar output, something like:

   +     17    g

in response to the "print" command. Upon receipt of this response, our software prepends the current date and time to the mass measurement value.

We do not attempt to support other functions which the lab scales provide, ranging from calibration to sensitivity adjustments. We do support a "tare" command.