How to Connect a Scale to a Computer: USB vs RS-232
Short answer: most scales connect to a computer by RS-232 (a 9-pin serial port) or USB. Check that your scale has the port or an interface option, use the right cable, and match the communication settings (baud rate, data bits, parity and stop bits) in the scale and the software. The easiest route on many A&D balances is a Quick USB interface such as the A&D FXi-02 ($98): press PRINT and the weight is typed into Excel, with no driver required.
Sending weights to a computer saves typing and typing errors, whether it is a shipping desk printing labels, a lab logging results, or a production line recording batches. MNM Scales has sold scales and interfaces for over 30 years, since 1992, and we are an authorized dealer for A&D, Sartorius, Mettler Toledo, Brecknell and CAS. Here is how to connect a scale to a computer, what you need for each connection, and how to fix the common problems.
USB vs RS-232: which connection do you need?
| Connection | How the computer sees the scale | Best for |
|---|---|---|
| RS-232 (serial) | A COM port; software reads the data stream | Lab software, LIMS, PLCs, older shipping and POS systems |
| USB, keyboard mode (Quick USB) | A keyboard; each reading is typed where the cursor is | Excel, Word, Notepad and web forms, with no driver |
| USB, virtual serial | A COM port over USB, after a driver is installed | Software written for RS-232, on PCs without a serial port |
| USB, POS HID | A point-of-sale scale device | Shipping and POS software that lists the scale model |
| Ethernet or Bluetooth | A network or wireless device | Scales away from the PC; offered as options on some models |
What you need
- A scale with an output: some scales have USB or RS-232 built in; on others it is an interface option, which is not included unless the listing says so.
- The right cable: a USB A-to-B cable, or a serial cable wired for your scale (straight-through or null modem). A USB-to-serial adapter (not included) adds a COM port to a PC without one.
- Software: your shipping, POS or lab software, a spreadsheet (keyboard mode), or a terminal program for testing.
- The scale manual: its function table sets the output format, the baud rate and when data is sent.
Step by step: connecting a scale to a PC
- Find the port. Check the back of the scale or the manual for USB, RS-232 (DB-9 or DB-25) or an option slot.
- Install the interface if your model uses an option card, then connect the cable to the scale and the PC.
- Set the output mode on the scale: send on PRINT key, send automatically when stable, or stream continuously.
- Match the serial settings (RS-232 and virtual serial): baud rate, data bits, parity, stop bits and handshake must be the same on the scale and the software. 2400 and 9600 baud with 7E1 or 8N1 are common, but use what your manual lists.
- Pick the COM port in the software; Windows Device Manager shows which port number the scale or adapter is on.
- Test it: place a weight and press PRINT, and check that the computer shows the same weight as the display.
Scales and interfaces for PC connection
| Product | Connection | Notes | Price |
|---|---|---|---|
| A&D FXi-02 Quick USB interface | USB, keyboard mode | For FX-i and FZ-i balances; cable included; no driver required | $98 |
| A&D EJ-02 Quick USB interface | USB, keyboard mode | For EJ series balances; no driver required | $88 |
| A&D SCE-02 Quick USB interface | USB | For SC and SE washdown scales | $99 |
| A&D SCE-03 RS-232C interface | RS-232C plus comparator relay output | For SC and SE washdown scales; cannot be installed together with SCE-02 | $129 |
| A&D KO-USB-AB cable | USB Type-A to Type-B, 6 ft | For devices with a USB Type-B port | $28.42 |
| Sartorius YCC01-USBM2 cable | RS-232 (25-pin) to USB | Confirm your balance model and connector before ordering | $179 |
| Mettler Toledo BC-60U shipping scale | USB and RS-232 | 150 lb x 0.05 lb, NTEP; 10 ft USB and RS-232 cables included | $726 |
| Brecknell PS-USB-150 shipping scale | USB and RS-232C | 150 lb x 0.05 lb, NTEP | $519 |
| CAS PDN-30 POS interface scale | RS-232C and USB | 30 lb x 0.005 lb, NTEP; works with POS systems; powered via USB | $589 |
Replacing a shipping scale? See Mettler Toledo PS60 vs BC-60 and our shipping bench scales. Reloaders connecting an A&D balance to a powder trickler can follow our FX-120i AutoTrickler setup guide.
Troubleshooting a scale-to-computer connection
- Nothing arrives: check the COM port number, the cable (a serial link may need a null modem cable), and that the scale’s output mode is on.
- Garbled characters: the baud rate, parity or data bits do not match between the scale and the software.
- Keyboard mode types nothing: click into the cell or field first; the reading goes wherever the cursor is.
- Readings arrive non-stop: the scale is set to stream; switch to send on PRINT or on stable.
- Software does not see a USB scale: check the USB mode (keyboard, virtual serial or POS HID) against what the software expects, and install the driver if the mode needs one.
- The scale shows an error: see scale error codes explained.
Calibration after setup
A data connection sends whatever the scale reads, so keep the scale itself calibrated. Choose in-house calibration with a certificate or NIST calibration with a NIST-traceable certificate. Mail-in calibration also covers scales bought elsewhere and is usually done within 1–3 business days after we receive the scale (see mail-in scale calibration), and in the Houston area we calibrate on-site for $295 plus $2 per mile, round trip, charged once per visit, with calibration priced per scale (see scale calibration in Houston).
Why buy from MNM Scales
- Interfaces, cables and PC-ready scales from A&D, Sartorius, Mettler Toledo, Brecknell and CAS, at live listed prices
- One of the largest scale distributors and an authorized dealer for the brands we sell, in business since 1992 (over 30 years)
- In-house calibration with a certificate, or NIST calibration with a NIST-traceable certificate; mail-in calibration also covers scales bought elsewhere and is usually done within 1–3 business days after we receive the scale
- TDA licensed with registered technicians; on-site service in the Houston area is $295 plus $2 per mile, round trip, charged once per visit, with calibration priced per scale
- Scale rentals of all types of scales
- Order pickup at our shop, 21249 FM 529 Rd, Cypress, TX, by appointment
- Phone answered 24/7 at (832) 290-3120
Not sure which interface fits your scale? Call us with the scale model and the software you use.
Frequently asked questions
How do I connect a scale to my computer?
Use the scale’s USB or RS-232 port, or add an interface option, connect the cable, set the scale’s output mode, and match the baud rate, data bits, parity and stop bits in your software. Then press PRINT to test.
Is USB or RS-232 better for a scale?
USB is easiest on modern PCs, especially in keyboard mode, which types readings into any program with no driver. RS-232 is common for lab software, PLCs and older systems, and works on newer PCs with a USB-to-serial adapter.
How do I get scale weights into Excel?
Use a USB interface in keyboard mode, such as A&D Quick USB. Click into a cell, press PRINT on the scale, and the reading is typed into the cell.
Why does my scale send garbled characters?
Garbled data usually means the baud rate, parity or data bits in the software do not match the scale’s settings. Set both to the same values listed in the scale manual.
Is the interface included with the scale?
It depends on the model. Some scales have USB or RS-232 built in; on others the interface is an option and is not included unless the listing says so.
Do I need a null modem cable?
Some scales need a null modem (crossed) serial cable and others a straight-through cable. Check the pin assignment in the scale manual.