A&D EJ-120 precision scale: Zero point calibration with the density determination kit

Some of the scales from A&D’s EJ series (known as “Newton” in the U.S.) can be equipped with an optional density determination kit (EJ-13), as shown in this photo provided by A&D:

The stainless steel weighing pan supplied with the scale is removed when the density determination kit is installed. Instead, a pan stand and a special double pan are used to weigh samples in the air and in a liquid.

The problem: these two parts weigh just 38.5 g, while the stainless steel pan weighs about 55 g, a difference of 16.5 g. The manual states, “the range for power-on zero is within ±10% of the weighing capacity around the calibrated zero point.”

For the EJ-120 with a capacity of 120 g, this is only ±12 g, so we can expect a “-E” underload error when the scale is turned on. After a few seconds, it will display a negative value, which annoyingly cannot be zeroed with the RE-ZERO key.

The solution: perform a zero point calibration after installing the density determination kit (no calibration weight is required).

Note: If you have not yet purchased an EJ series scale, consider purchasing one with a higher capacity to avoid this problem.

EJ-120 scale zero point calibration

Open the calibration switch cover on the bottom of the scale:

Remove the stainless steel weighing pan and install the density determination kit as described in the manual:

Switch on the scale and wait until a value is displayed (this can take a few seconds):

Press and hold the calibration switch until the scale displays “CAL 0” (then release):

Confirm the zero point with the [PRINT] key. The scale displays “100.00” (the required calibration weight for the next step, which we will skip):

Press the [ON/OFF] key to switch off the scale.

If you now turn the scale on again, it will display “0.00 g” with the density determination kit installed.

Note: Clever readers may have noticed that the total zero range of 24 g (±12 g) exceeds the 16.5 g weight difference. Therefore, it is possible to perform a zero calibration at a point where the EJ-120 scale automatically zeroes either with the density determination kit or with the stainless steel pan installed. However, this might not work reliably for long because factors such as temperature changes affect the zero point (which is the reason that the zero range exists).

Links to the EJ series on A&D’s websites:

Where to find weighing industry news

In this post I will attempt to compile a list of news sources and news gathering strategies for the weighing industry. This is a work in progress, please do not hesitate to leave a comment with additional (good quality) sources and ideas.

Manufacturers and dealers

An obvious starting point are the websites of weighing equipment manufactures. Many have a news page that you can check periodically. This task can be automated with software or services that monitor websites and notify you of changes. Some websites may also still offer RSS news feeds.

While websites of weighing equipment dealers are rarely an original source of industry news, they can be helpful in finding additional manufacturers as dealers usually indicate which brands they sell.

Specialized weighing news websites

A good example (and the only one I am currently aware of) is the Weighing Review Portal, which also publishes the Weighing News newsletter.

Industry associations, regulatory bodies and similar organizations

Social media

LinkedIn is the most promising candidate: Other than companies and individuals, you’ll also find groups such as Weighing, Automation & Process Control Industry Professionals and Weighing Systems 4.0. One downside of LinkedIn are the motivational quotes and the tons of LinkedIn cringe you may encounter.

Sometimes Facebook and Twitter offer different content from LinkedIn. Depending on the country, other social media platforms may be more popular.

YouTube is also considered a social media platform, but the most popular videos about weighing equipment that you’ll find there are primarily made for entertainment purposes. However, if you’re interested in a specific device or niche category of weighing instruments, it can still be worthwhile to do a search.

Google Alerts

Once you’ve entered a search term (e.g. the name of a weighing equipment manufacturer), this service will alert you by email when it finds new matching results on the internet. In order to keep the quantity and quality of the alerts at a manageable level, I recommend restricting the frequency to once per week (or less) and choosing only the most relevant results.

Trade fairs

Aside from the current pandemic, the biggest challenge with trade shows is that weighing instruments are used in almost every industry and span a wide range from consumer goods over medical devices to industrial solutions. Trade shows that exclusively feature weighing instruments are therefore the exception. If and when the situation returns to normal, I will compile a relevant list.

Ohaus Defender 3000 scales: Commands to request the weight (and to control the scale).

The Ohaus Defender 3000 series scales with T32XW and T31P indicators can send the weight via the standard RS-232 interface. There are several ways to trigger data transmission:

  1. By pressing the print button1 on the scale,
  2. automatically at each stable weight,
  3. continuously2 at a rate that depends on the baud rate (approx. 50 values/s with standard setting 9600 bit/s; 100 values/s with 19200 bit/s)3,
  4. in intervals from 1 s to 3600 s,
  5. on demand via the interface with a suitable command (bidirectional communication).

In this article I’ll describe the 5th method: a device connected to the balance via the RS-232 interface (e.g. a computer, microcontroller, PLC, etc.) sends a command to the balance and it responds with the weight:

Requesting the weight from an Ohaus Defender 3000 scale
Made by me with Microsoft Whiteboard, an application that fits my limited artistic talent

Notes:
1 Originally, scales were more often connected to printers than to computers, hence the name “Print”.
2 Continuous transmission (3) is not possible with verified (legal-for-trade) scales.
3 The actual measuring rate (conversion rate) is always approx. 16 values/s.

All explanations in this article refer to the current (October 2021) generation of the Ohaus Defender 3000 with the T32XW indicator with firmware 1.03 (left in photo above) and the T31P indicator with firmware 1.14 (right in photo).

Instruments with different firmware as well as older or possible future newer Defender 3000 models may behave differently. For verified (LFT) scales, some features are disabled (also, legal requirements must be observed when connecting verified scales to computers).

Commands to request the weight and data format of the response

To send commands to the scale and to view the reply, you can use any serial terminal software (I’ll be using HTerm). No settings need to be changed on the scale: by default, data transmission by pressing the print key (1) and requesting the weight via the interface (5) is supported.

Important: In HTerm, be sure to select “CR” or “CR-LF” in Send on Enter under Input Control so that all commands sent to the scale are terminated with these characters (required).

The following commands are listed in the user manual (PDF), I’ll discuss them in detail below:

Defender 3000 scale commands

SP command (Print when stable) – does not work as expected

If the scale sent the weight as soon as it stabilized after receiving SP, this command would be very interesting. However, the Defender 3000 does something completely different: it sets the Print > Stable setting to “On” and responds with “OK”:

SP command Ohaus Defender 3000 scale

As far as I know, this setting cannot be changed back to “Off” with any command (except the Reset command). It must be changed directly on the indicator in the Print menu.

This command is unfortunately useless for retrieving the weight. On other scales, such as the Ohaus Defender 5000, it works as expected.

P command (Print)

The P command corresponds to pressing the Print button on the scale. Therefore, the already mentioned stability setting (Print > Stable) is observed:

Print > Stable: “On”

If Print > Stable is set to “On”, the weight is only sent if it is stable (an asterisk * appears in the upper left corner of the display when the weight is stable). If the scale receives the P command when the weight is unstable, it does not respond (and the display briefly shows “–NO–“):

P command Ohaus Defender 3000 unstable print stable on

Note: For verified scales, Print > Stable is always set to “On” and cannot be changed.

Print > Stable: “Off

If Print > Stable is set to “Off”, the scale always responds to P with the weight. Unstable weights are marked with a question mark (see below).

Output format of the scale when replying to the P command

The description in the manual is largely correct:

Defender 3000 scale output format

The 7 characters for the weight correspond to the 6 digits of the scale display plus the decimal point. The legend is only used for the gross, net and tare weight (deactivated by default) and is otherwise omitted.

Example 20.00 kg, stable:

P command Ohaus Defender 3000 scale stable

Example -3.18 kg , unstable:

P command Ohaus Defender 3000 scale unstable

Example 11,87 kg, unstable, with unit (Print > Content > Unit: “On”):

P command Ohaus Defender 3000 scale unit unstable

Example with gross, net and tare weight as well as unit (all entries in the Print > Content menu set to “On”), stable:

P command Ohaus Defender 3000 gross net tare weight unit stable

Note: The scale sends the lines with the net weight and the tare value only if the latter is not zero (i.e. if the tare function was actually used).

Same example as above, except that the tare value was set with “1000T” via the interface:

P command Ohaus Defender 3000 gross net pre-tare weight unit stable

The only difference is “PT” (pretare) instead of “T” in the last line.

IP command (Immediate Print)

The IP command can be used only with non-verified scales. After receiving the IP command, the scale sends the weight immediately, whether it is stable or not. Moreover, the response is not influenced by settings in the scale’s menu, so Print>Stable and Print>Content do not play any role.

Output format of the scale when replying to the IP command

For a stable weight, the response consists of 16 characters:

IP command Ohaus Defender 3000 stable

If the weight is unstable, two characters are added (space and question mark at the end):

IP command Ohaus Defender 3000 scale unstable

Other commands

CP (Continuous Print)

Activates the continuous transmission of the weight (possible only with non-verified scales), see point 3 at the beginning of this article. With 0P (zero + P) this can be deactivated again. The data format is similar to those described above.

Caution: The high data rate can overload some programs. In addition, the scale is sometimes falsely recognized as a serial mouse by Windows if it sends values continuously already at system startup (the mouse pointer then jumps wildly across the screen and your customer may call you and complain that your scale made his PC go crazy).

xP (Interval Print)

Transmission every x seconds (with x from 1 to 3600), send 0P to disable. The data format is the same as the P command.

Z (Zero)

For zeroing the scale, corresponds to pressing the Zero button on the indicator. The allowed range for executing the command is controlled by the Setup > Zero setting (2% or 100% of the capacity).

Note: The scale always responds with “OK”, even if the allowed range has been exceeded and the command could therefore not be executed (and the display showed “–NO–“).
Caution: If Setup > Zero is set to “0-100”, the maximum capacity could be unintentionally exceeded (as the zero range is not subtracted from the capacity).

Use the Z command to eliminate small residual values. It is not intended as an alternative to the tare command (see below).

T (Tare)

Same as pressing the Tare button. Suitable for “zeroing” the weight of a container or weighing individual components of a recipe.

The tare function can be deactivated by sending 0T (zero + T). The scale will then show the gross weight again instead of the net weight (only possible via this command, not via a button on the indicator). 0T is probably not supported by verified scales (I haven’t tried this out yet).

Note: If the tare function cannot be executed (because there is no object on the scale), the scale will still respond with “OK”, but will show “–NO–“in the display.

xT (Pre-tare)

Sets x as a pre-tare value, where x must be specified in g. Not possible with verified scales.

Example:

1000T command pre-tara Ohaus Defender 3000 scale

PU (Print Unit)

The scale responds with the currently used unit (without blank spaces, see example under xU).

xU (Unit)

Changes the current unit, 1U=>g, 2U=>kg, 3U=>lb, 4U=>oz, 5U=>lb:oz.

Important: In order to set a unit, it must have been activated in the menu of the scale under Mode > Unit. Otherwise, the scale responds with “ES” instead of “OK”:

unit grams not activated

Verified scales may not support all units (this depends on your local regulations).

Example switching from kg to g:

Change unit to grams

PV (Print Version)

The scale responds with the type of indicator (T32XW or “Defender 3000” for T31P), the firmware version (Sr=Software Release) and the “legal-for-trade” setting (“ON” for verified scales, “OFF” otherwise). With this command you can easily check if your scale uses the same firmware as my test unit.

Example T32XW:

PV command Ohaus Defender 3000 T32XW

Example T31P:

PV command Ohaus Defender 3000 T32XW

<ESC> R (Reset)

Resets all settings to the factory defaults. In my tests, some settings were only applied after a restart. I see no reason to use this command during normal operation (though – unlike on the Ranger 3000 and 4000 – it fortunately didn’t seem to reset anything in the CAL menu).

Example:

Reset command Ohaus Defender 3000

Summary of how to request the weight from an Ohaus Defender 3000 scale

The IP command is the simplest way to retrieve the weight (with the unit) from the Defender 3000. However, it cannot be used with verified scales.

Alternatively, the P command can be used, which is equivalent to pressing the Print button. It is influenced by the Print > Stable setting (send only stable values) and Print > Content setting (scope of transmitted data and unit).

SP is not a command to retrieve the weight, even if the description in the manual suggests this.

The format of the scale’s response differs slightly depending on the command (I don’t know why). I therefore recommended not reading a fixed position from the response string, but searching for the first number instead (which will be the weight).