Using Ohaus Defender 3000 Scales with BarTender

In this article, I’ll show you how to capture the weight (and tare weight) from an Ohaus Defender 3000 scale using BarTender while avoiding an issue that would otherwise lead to the scale showing only “Print” on its display.

Notes:

This guide applies to the new generation of Ohaus Defender 3000 scales launched at the end of 2021/beginning of 2022. The picture below shows the new indicator on the right and its predecessor on the left.

Ohaus Defender 3000 indicators: Old model on the left, new one on the right.

It was created using Bartender Designer 2022 R8 and version 1.04 of the Ohaus Defender 3000 firmware. Future versions might make things easier (or more difficult, as seems to be the general trend).

Can you use existing Ohaus scales defined in BarTender?

Let’s try it out. In the menu, go to Administer > Weighing Scale Setup:

BarTender Weighing Scale Setup

If no scale has been defined yet, this will launch the Add Scale Wizard (otherwise, click on Add Scale in the windows that appears):

BarTender Add Scale Wizard

After clicking next, you’ll be able to select “Ohaus” as the manufacturer and you’ll see a number of supported models. Select “Ohaus 3000 Series” (as this sounds most similar to “Ohaus Defender 3000 series”):

BarTender Add Scale Wizard Ohaus scales

Continue by specifying the connection method. If your scale is connected via USB or RS-232, you’ll also have to choose the COM port and confirm the interface parameters (Flow Control is set to XON/XOFF by default, it doesn’t really matter):

Click next on all further steps of the wizard. After completing it, we can now test the scale. Select it and click on Properties:

In the window that opens, switch to the Connection tab, then click on Test Connection:

Bartender will start sending the “IP” (Immediate Print) command to the scale to request the weight. It does so multiple times per second (4 times by default). It seems to capture the net weight correctly (5.005 kg in the screenshot below):

However, there are at least two issues with this method.

1. The scale shows “Print” all the time

When the scale receives the “IP” command, not only does it reply by sending the weight, but it also shows “Print” on its display. As BarTender sends this command multiple times per second, “Print” is all that you’ll see:

My opinion: Displaying “Print” when the user presses the Print button on the scale is useful (it gives the user feedback). Displaying it when the “P” command is received can be justified by saying that the scale should behave just as if the user had pressed the physical button. However, displaying it when the scale receives “IP” does not make much sense to me. I’m hoping Ohaus will reconsider this and change it in a firmware update. Until then, you can use the solution described below.

2. You cannot use a tare weight

The second issue I found is that once you’ve used the scale’s tare function, BarTender is no longer able to capture the net weight (and it also can’t capture the tare weight):

Solution: Define a new scale that uses the MT-SICS protocol

Unlike its predecessor, the new Defender 3000 supports (some) MT-SICS commands. The MT-SICS equivalent to the “IP” (Immediate Print) command is the “SI” (send immediately) command1. Fortunately, the scale replies to this command without displaying “Print”. Moreover, it also supports the “TA” command that BarTender uses with MT-SICS Level 1 scales to request the tare weight.

Note: You can explicitly set the scale to “SICS” by going into the “Print” menu (for RS-232) or “Print1” (for USB or Ethernet) and setting “Assignment” to “SICS”, but this was not necessary in my tests.

Let’s start the Add Scale Wizard again, but this time, you don’t select an existing model. Instead, choose Define a model not listed above:

Define a new scale model

Then, select Ohaus as the manufacturer and enter a name for your new model, e.g. “Ohaus Defender 3000 SICS”. Under Protocols Supported by this Scale, select “Mettler Toledo (MT-SICS Level 1)”:

Continue with the Wizard as before.

I used this opportunity to test the optional Ethernet interface of the new Ohaus Defender 3000. I set it to acquire an IP address via DHCP (which is out of the scope of this tutorial), connected it to our network and then copied its IP address from the menu under Ethernet/IP Address. The port (which is also displayed by the scale) is always 9761:

Specify scale connection in Bartender: TCP/IP Network Port

You can – of course – still connect to the scale using a COM port.

After completing the Add Scale Wizard, it is again time to test the connection. Click on Properties:

Installed Scales: Ohaus Defender 3000 SICS

In the new window, switch to the Connections tab and click on Test Connection:

You’ll now see that the net weight and tare weight are acquired correctly:

Ohaus Defender 3000 current weight shown in BarTender

Furthermore, the scale’s display now shows the weight instead of just “Print”.

Conclusion

The new Ohaus Defender 3000 scales are compatible with BarTender, but initial setup is not quite as straightforward as one might expect. You’ll get the best results by defining a new scale that uses the MT-SICS protocol (which the new Defender 3000 supports, unlike its predecessor).

I hope this tutorial is helpful. Please don’t hesitate to leave a comment, but please note that I am in no way a BarTender expert and that answering BarTender-related questions is not something I particularly enjoy. I suggest using the BarTender’s Online Help system or contacting Seagull Scientific if you need support with their software.


  1. Well actually, the equivalent would be “SIU” (send immediately in display unit), but this article is long enough and “SI” is the better choice anyway. ↩︎

RS-232 Basics (Part 1): Scale Pinout and Cable Wiring

RS-232 has been around since the 1960s, so it seems appropriate to start this article with a communication method that’s even older: the tin can phone.

The kid on the left is speaking into a can held in front of their mouth (transmitting data, TD), while the other is listening through a can held to their ear (receiving data, RD).

To enable both kids to speak (TD) and listen (RD) at the same time, they would require a second set of cans connected by a string, represented by the red arrow1. Let’s also mark the ground (GND) in green:

At this point, the illustration looks similar to what you might find in the RS-232 section of your scale’s user manual2:

RS-232 schematic: Scale to PC connection using a crossed cable

To establish bidirectional communication with this scale, you would need to connect the transmit data pin (usually called TD or TXD) to the receive data pin of your computer (RD or RXD) and vice versa. Additionally, it’s essential to connect the ground pins (GND) for reference3.

Although this seems simple, attempts to establish communication with a scale using RS-232 often fail at this basic stage.

To understand why this is such a common problem, take a look at the photos of the RS-232 interface of A&D’s popular FX-120i balance and Radwag’s PUE C32 weighing indicator:

Both weighing instruments have a male D-sub port with 9 pins (DE-9M, frequently but incorrectly called DB-9M)4. You might therefore think that they can use the same cable. You would be wrong, as their pinout is not identical:

Radwag’s PUE C32 receives data (RD) on pin 2 and transmits it on pin 3 (TD), requiring a crossed cable when connected to the standard DE-9M port of a PC. A&D’s FX-120i receives data on pin 3 (RD) and transmits it on pin 2 (TD). It requires a straight cable.

RS-232 cable terminology

Null modem cables are also known as crossover or crossed cables. They cross-connect certain pins, such as RD and TD.

Straight cables run straight through and are also called straight-through cables or 1:1 cables.

There are other types of serial cables, but these two are most common.

If you use the wrong type of cable, you connect TD to TD and RD to RD. This would lead to a situation like the one illustrated below, where both kids are holding the cans to their ears and no communication is possible:

While we can immediately recognize that something is wrong in this picture, no one can tell a straight cable from a null modem cable just by looking at it:

Key takeaways: The fact that you can plug in a cable means nothing – it’s the pinout of your weighing instrument and the wiring of your cable that matters.

If the electrical connection between your scale and computer is not established correctly, it does not matter which software you use. It will not receive any data.

There are many more aspects of RS-232 communication to explore – we’ll do that in future articles. In the meantime, don’t hesitate to leave a comment, but please understand that I can’t remotely diagnose communication problems for free.


1Bidirectional communication on a single string is technically possible but doesn’t seem very practical.

2Did you notice that this schematic doesn’t tell you the gender of the port (DE-9M or DE-9F)? While it was just a simplified example, many actual user manuals omit this information as well, adding to the general confusion surrounding RS-232.

3Some scales and balances require connections between other pins. This is an advanced topic for a future article.

4RS-232 ports on scales come in many different forms and are not limited to DE-9M. You’ll frequently encounter DE-9F, DB25 (especially on older balances), RJ11, RJ45, and many others.

Using verified Ohaus SJX scales with our software

Most class I and II weighing instruments use what is called an “auxiliary indicating device” with a “differentiated scale division”1: On the display, the final digit or digits are visually distinct from the others. This is also the case with Ohaus SJX scales that have been verified (e.g. the SJX6201M):

Note how the scale division (d) is one tenth of the verification scale division (e) when weighing in g

This digit is enclosed in square brackets when the weight is sent over one of the optional interfaces (such as RS-232, USB, or Ethernet). Example:

   1234.[5]     g

By default, our software does not capture a digit that comes after a non-numeric character. This can be easily fixed in two steps. We’ll use screenshots from Simple Data Logger as an example, but the procedure is basically the same for our 232key virtual keyboard wedge software2.

1. Change the regular expression used to capture the weight

In the Input tab, click the Customize button and replace the regular expression with the following one:

(-*[0-9]*\.?[0-9]*\[[0-9]+)

This will ensure that the opening square bracket and the last digit are also captured (shown in blue in the Event Log):

Remove the bracket

The string we’ve now captured is not a number because it contains a bracket. Writing it to a file like this would make things complicated when processing the data later.

Fortunately, you can easily remove the bracket: Go to the Process tab, check Enable Editing, and enter the opening square bracket “[” in the Remove characters field:

SDL will now properly write the complete weight as a number to the CSV file, which can be opened in Excel or other programs:

Important: If you are utilizing our software in connection with a verified scale, please ensure that such usage is compliant with the regulations and requirements of your local jurisdiction.


1: See OIML R76 (PDF) for further information
2: For an example that uses 232key, see this article