For some of my coffee roasting experiments I wanted a scale I could connect to a PC or Mac. I looked at many scales and the Ohaus Scout® Pro Balance series was a nice blend of capability vs price. This series is designed for educational applications. RS232 (part 71147376) and USB (part 71147377) interfaces are available. This article documents the use of the USB interface. I assume the RS232 is identical as the user manuals appear identical except for how to connect to the computer.
For my application the SPE2001 was the choice with a 2 Kg capacity and 0.1g readability.
Of particular interest to my work is the integrated weigh below hook so that I can suspend the weight.
Setup is simple:
4. Plug in the AC adapter
Connecting to the PC/Mac
Installing the USB adapter and plugging into the PC causes the scale internal menus to offer the USB/RS232 options. The system defaults to 2400 baud, 7 data bits, no parity, 1 stop bit, no flow control. All of this is changeable via the 2 button menu. The default unit of weight is grams so no modifications were required for my work. Also when the USB adapter is active Auto-off is turned off so the scale can be used for long term capture.
An included driver mini-CD was not required during installation. When I plugged the USB cable to my Windows 7 machine the serial driver was auto loaded. I have not tried on my Mac yet but my experience is the USB to serial adapters tend to have native support in the OS.
My initial work is on the Win 7 PC as that is what I use with Artisan for monitoring my roaster. While there are several commercial data loggers, I found two free ones that work nicely for my requirements.
RS232 Data Logger captures data send from the scale to a data file. Terminal can send commands to the scale as well as log data.
Serial Data Output
· = blank
In this example weights in grams captured every 10 seconds.
Output String Format
• Weight – 12 characters (right justified)
(Note: The manual says 10 but results both from Terminal and RS232 Logger showed 12)
• units – 5 characters (left justified)
• Stability – blank when stable, ? when unstable
• time if in interval capture mode – hh:mm:ss
Programming the Scale
Several factors contributed to the selection of this scale. Many scales could only be programmed via the buttons on the scale. The commands mean a front end macro can be created that configures all conditions as well as starts the capture. The set of commands include:
|?||Print current mode (g = grams)|
|0A||Turn auto-print off (zero A)|
|10A||Auto print every 10 seconds (any int from 1 to 3600)|
|0M||Gram units mode (zero M)|
|LE||Print last error code (e.g. Err 0)|
|0S||print unstable data (zero S)|
|1S||print stable data only|
|CR or CRLF||execute the command|
By using the nA command the scale can do the timing so that a new reading is captured regularly from one second to one hour (1-3600 seconds). This means the data logger program is passively capturing and logging the data. Limited values of Auto-Print are available from the menu: 0, 5, 15, 30 and 60 seconds. For other values a serial command is required.
A UPS will be required in my experiments as they will run for days. If power is lost when it is restored the scale will auto tare on power-up. This will require that the weight be removed, the scale turned on, the weight rehung and the commands resent.
Question: IF power is lost and batteries are in the scale will it just fall back to battery power without stopping? This could work with a notebook computer that could stay self powered for hours avoiding the UPS.
Question: In terminal.exe and RS232 Data Logger are each entry written to disc when received so that if the power is lost of program about the data is not lost?
Answer: terminal.exe does not log to disk regularly. Only when the StopLog button is pressed. RS232 Data Logger does write to the disk file every 30 seconds so it is safer for long running experiments. Many of mine will run for days.