Ohaus 5 - Digital Scales Blog

Ohaus Ranger 7000: can a scale simplify complex weighing applications?

“Simplifying even the most complex industrial applications” is the claim that Ohaus makes in their data sheet. Is it justified? After spending some time trying out the different functions of this scale, I believe that yes, it is.

The key to understanding the power of the Ohaus Ranger 7000 scales are the 10 application modes:

Weighing: Determine the weight of items (no surprise here). A statistics feature can be used in weighing mode to calculate statistical data.
Counting: Count parts of uniform weight. Auto-optimization recalculates the average piece weight as the number of pieces is increased.
Check weighing and check counting: Compare the weight or count of a sample against target limits. Connect with discrete I/O option kit to use external check lights.
Formulation: For compounding and recipe making. Compensation can be used in case a component is overfilled (outside the tolerance).
Percent weighing: Measure the weight of a sample displayed as a percentage of a pre-established reference weight.
Filling: Fill a container to a target weight. Progress bar displays filling status. Connect with discrete I/O option kit to control a semi-automatic filling system.
Dynamic weighing: Weigh an unstable load. Scale takes an average of weights over a period of time. Can also be used as a display hold function.
Density Determination: Determine density of solids.
Differential weighing: Calculate the difference between sample weights and initial weights.
Sieve analysis: Used to assess the particle size distribution (also called gradation) of a granular material.

Each application is displayed differently on the 4.3 inch color screen. Compare, for instance, the display in weighing mode to check counting mode:

Weighing application on Ohaus Ranger 7000 scale — Weighing

Check counting application on Ohaus Ranger 7000 scale — Check counting

The applications are not limited to different presentations:

Five physical smart buttons below the display take on different functions depending on the application.
All settings relevant to the current application can be accessed easily by pressing the settings button.
The internal library allows you to save application specific data for commonly used items (e.g. the target weight and tolerance for check weighing, the average piece weight in counting mode or the set points in filling mode). The scale can be connected to a bar code reader to simplify recalling data from the library.
An optional I/O kit with four outputs (relays) and 2 inputs can be used to integrate the scale with external devices. The functionality is again dependent on the application mode. One of our customers has used the filling application with the I/O kit to build filling machines controlled entirely by a Ranger 7000 scale.

Therefore, as long as your application is supported by the scale, it does an excellent job at simplifying many tasks.

Raspberry Pi: Connecting a scale can be very easy…

…as long as you choose the right scale! The photo below shows an A&D EK-2000i compact balance connected to a Raspberry Pi 3 Model B using a compatible serial cable and an FTDI RS-232 to USB converter:

Python and pySerial make it easy to read weight data from a scale

On the Pi, I used Python with pySerial to read the weight from the scale. The script I put together is trivially simple. You can download it here or just type it on the Pi:

By pressing the PRINT-Button on the scale, I then sent a few weight values to the Pi and the script wrote them to the terminal (b’ is added by Python):

In a more useful application, you would want to parse the data sent from the scale to get the weight as a number and then do something with it (maybe write it to a database). You could also do interesting things with the GPIO on the Pi like sounding an alarm when a certain weight is exceeded (though a microcontroller might be better suited for this).

I then switched the scale to “stream mode” (continuous transmission) where it sent 10 values per second (stable or not). The output you see below is the result of placing a single object on the scale and waiting for it to stabilize:

I hope this example shows that it can be really easy to transfer the weight from a scale to a Raspberry Pi.

Notes on scales and the Raspberry Pi

One advantage of A&D scales is that (almost) all of them use the same data format and interface parameters and that you’ll find a good description in the manual:

However, you could use also use scales made by other manufacturers as long as they come with an RS-232 interface and the ability to send the weight in ASCII format. Available data output modes vary, so please read the product description carefully before buying.

A converter like the one I used is already built into some scales, which means that you can directly connect them to the Raspberry Pi via USB (you won’t need a serial cable). You’ll find many Ohaus scales with this interface option and the ones I’ve tested worked fine. However, cheaper scales with a USB interface can often not be used with pySerial as they do not emulate a serial port. They can also present other challenges (e.g. data that is not transmitted in human-readable ASCII format).

You do of course not have to use Python, just make sure that your preferred programming language can communicate over a serial port on the Pi. The book Raspberry Pi with Java: Programming the Internet of Things (IoT) contains projects using Ohaus scales and, well, Java.

Finally, please don’t try to use the serial interface already provided by the Pi on the GPIO pins without a logic level converter (RS-232 voltage could reach up to 15V). Excellent further information on serial ports on the Raspberry Pi can be found here.

Photo: Ohaus Navigator product range

Ohaus Navigator (NV), Navigator XL (NVL) and Navigator XT (NVT) scales – what’s the difference?

Physical dimensions

While all scales in the Ohaus Navigator product range are fairly compact, their dimensions vary according to the series to which they belong. In our photo, you’ll see the Navigator XT (NVT) on the left, the narrow and lengthy Navigator XL (NVL) in the middle and the smaller Navigator (NV) on the right:

The Navigator (NV) is the only one with different platform shapes within the series: The NV212 – the only scale with 0,01g readability in the entire range – has a round platform as shown in the picture while higher capacity scales have a platform which is similar to the other series.

Dimensions (width x length x height in mm)

Navigator XT (NVT): 240 x 249.5 x 69.8
Navigator XL (NVL): 204 x 282 x 74
Navigator (NV): 204 x 212 x 58

Options

All scales can use the same interface options (RS-232, USB or Ethernet) as they have the same option slot on the bottom. The photo provided by Ohaus shows the Navigator XL (NVL) with installed USB interface:

However, only the Navigator XL (NVL) and XT (NVT) series have room for an optional rechargeable battery:

The scales can also be used with non-rechargeable batteries (4 size AA batteries for the NV and 4 sice C batteries for the NVL and NVT).

Performance

All scales stabilize quickly (within one second according to Ohaus) and perform similarly:

Model	Repeatability	Linearity	OCL
NV212	2 d	± 2 d	± 3 d
NV511	2 d	± 2 d	± 3 d
NV1101	2 d	± 2 d	± 3 d
NV2101	2 d	± 2 d	± 3 d
NV4101	2 d	± 2 d	± 3 d
NV5101	2 d	± 2 d	± 3 d
NVL511	2 d	± 2 d	± 3 d
NVL1101	2 d	± 2 d	± 3 d
NVL2101	2 d	± 2 d	± 3 d
NVL5101	2 d	± 2 d	± 3 d
NVL10000	2 d	± 2 d	± 3 d
NVL20000	2 d	± 2 d	± 3 d
NVT1601	2 d	± 2 d	± 3 d
NVT3201	2 d	± 2 d	± 3 d
NVT6401	2 d	± 2 d	± 3 d
NVT10001	2 d	± 2 d	± 3 d
NVT16000	2 d	± 2 d	± 3 d

The values are expressed in scale intervals (d, difference between two successive indications, often also referred to as “(display) division” or “readability”). OCL stands for off center load. To minimize the OCL error, place the weight in the center of the platform. Approved models are not included in the table as their availability varies by region.

Tag: Ohaus