peter-tanner.github.io/_posts/2024-10-06-Opening-sig-files-from-LDS-Dactron-shaker-table-machines-in-Python.md

---
title: Opening .sig files from B&K LDS shaker table machines in Python
author: peter
date: 2024-10-06 16:59:44 +0800
categories: [Programming, Mechanical] # Blogging | Electronics | Programming | Mechanical | SelfHosting
tags: [python, com, 32-bit, tip, shaker table, B&K] # systems | embedded | rf | microwave | electronics | solidworks | automation | tip
# image: assets/img/2024-10-06-Opening-sig-files-fr/preview.png
---

## Introduction

Brüel & Kjær have a [line of electrodynamic shaker tables](https://www.hbkworld.com/en/products/vibration-testing/shaker-systems#!ref_bksv.com) that use their LDS Dactron signal analyzer which produce proprietary `.sig` files.

Example of a `.sig` file's header:

```bash
$ xxd input1\(t\).sig  | head -n 10
00000000: 44f7 0000 0744 4143 5452 4f4e 5804 0000  D....DACTRONX...
00000010: 0100 0000 0004 0000 0100 0000 0004 0000  ................
00000020: 0100 0000 0100 0000 0004 0000 0969 6e70  .............inp
00000030: 7574 3128 7429 0969 6e70 7574 3128 7429  ut1(t).input1(t)
00000040: 0969 6e70 7574 3128 7429 0156 0156 0000  .input1(t).V.V..
00000050: 1253 6570 7465 6d62 6572 2032 362c 2032  .September 26, 2
00000060: 3030 3608 3130 3a35 373a 3338 0856 5055  006.10:57:38.VPU
00000070: 2d32 3232 3200 0000 0000 0000 00a5 e2ec  -2222...........
00000080: c367 d805 3f00 0000 0000 0000 0000 0000  .g..?...........
```

As shown in the [user manual for their PC software](https://www.bksv.com/downloads/dactron/shakercontroller/manuals/shakercontroluserguide6.3.pdf), they provide an ActiveX Signal Reader which provides some functions to enable the `.sig` file to be opened in "Visual Basic, MATLAB, LabView, C++ and so on".

## Tutorial on how to use in Python

1. Download [Shaker Control](https://www.bksv.com/en/services/downloads/vibration-control-software/version-9). While a license key is required to use the software, we only need the `DactronSignal.dll` file.
2. Install the software to a directory of your choosing, I think it installs in `C:\Program Files (x86)` by default but I am not sure since I chose to install it to `D:\Programs`. Annoyingly you do need to install the program, inspecting the installation files in 7-zip doesn't show this DLL specifically.
3. Go to `Bruel and Kjaer\LASER and COMET Vibration Control\Shaker Control LaserUSB\bin` and copy `DactronSignal.dll` to a directory of your choosing.
4. Create a command prompt and `cd` to the directory containing the DLL and register the DLL:

```bat
regsvr32 .\DactronSignal.dll
```

After copying the `DactronSignal.dll` file to another directory you may uninstall the program.

The `Bruel and Kjaer\LASER and COMET Vibration Control\Signal Reader` directory contains examples for Visual C++ and MATLAB. There are also some sample `.sig` files.

5. Create a **32-bit** Python virtual environment and activate the virtual environment OR use a **32-bit** Python installation. It must be 32-bit since the DLL is 32-bit, if you use 64-bit it will not find the class, and you will get this error:

```powershell
PS C:\<path>\signal_reader> python
Python 3.9.6 (tags/v3.9.6:db3ff76, Jun 28 2021, 15:26:21) [MSC v.1929 64 bit (AMD64)] on win32
--- ✂
PS C:\<path>\signal_reader> python .\test.py
--- ✂
pywintypes.com_error: (-2147221021, 'Operation unavailable', None, None)

During handling of the above exception, another exception occurred:
--- ✂
pywintypes.com_error: (-2147221164, 'Class not registered', None, None)
PS C:\<path>\signal_reader>

```

6. Install `pywin32` (and `numpy` and `matplotlib` for plotting)

```powershell
python -m pip install pywin32
python -m pip install numpy matplotlib
```

7. Create a script to see if loading the DLL works. Use the provided `FFT1(f).sig` file for testing:

[⬇ Download `FFT1(f).sig` for testing this script](</assets/lib/2024-10-06-Opening-sig-files-fr/FFT1(f).sig>)

```python
import win32com.client
import numpy as np
import matplotlib.pyplot as plt

dac_signal = win32com.client.Dispatch("SignalReader.DacSignal.1")

success = dac_signal.LoadSignal("FFT1(f).sig")

if success:
    print("Signal loaded successfully")
else:
    print("Error loading signal")
    exit(1)
```

[⬇ Additional file: `G1,1(f).sig`](</assets/lib/2024-10-06-Opening-sig-files-fr/G1,1(f).sig>)\
[⬇ Additional file: `input1(t).sig`](</assets/lib/2024-10-06-Opening-sig-files-fr/input1(t).sig>)

8. If it loaded successfully, you may try the following script which was adapted to Python from the example MATLAB script given in the documentation `Recall_and_plot_G11.m`. This should provide the following plot:

![FFT1(f).sig plot](/assets/img/2024-10-06-Opening-sig-files-fr/plot_fft.png)

```python
import win32com.client
import numpy as np
import matplotlib.pyplot as plt

dac_signal = win32com.client.Dispatch("SignalReader.DacSignal.1")

success = dac_signal.LoadSignal("FFT1(f).sig")

if success:
    print("Signal loaded successfully")
else:
    print("Error loading signal")
    exit(1)

# Get slice number of the signal, for G1,1(f) signal, the value is 1.
nSliceNum = dac_signal.NumofSlice
# Get number of samples.
nNumofSamples = dac_signal.NumOfSamples

# slice index is 0 based
indexSlice = 0
# Sample index is 0 based
indexFirstSmp = 0

# Get X Begin
xBegin = dac_signal.XaxisBegin
# Get X Delta
xDelta = dac_signal.XaxisDelta
xSpacingEven = dac_signal.XaxisSpacingEven

varX = np.zeros(nNumofSamples)

if xSpacingEven == 1:
    # When X-axis is evenly spaced, generate values with X(i+1) = X(i) + XDelta
    varX = np.arange(xBegin, xBegin + xDelta * nNumofSamples, xDelta)
else:
    # When X-axis is unevenly spaced, generate values with X(i+1) = X(i) * XDelta
    for i in range(nNumofSamples):
        varX[i] = xBegin * (xDelta**i)

# Get Y data (first slice)
varY = dac_signal.GetData(indexSlice, indexFirstSmp, nNumofSamples - 1)

# Convert varY from a COM array to a numpy array
varY = np.array(varY)

# Get data type (1: real, 2: complex)
DataType = dac_signal.DataType

# Plot the data based on the data type
if DataType == 1:  # Real data
    plt.figure()
    plt.loglog(varX, varY)
    plt.title("Real")
    plt.xlabel("X")
    plt.ylabel("Y")
    plt.grid(True)
    plt.show()
else:  # Complex data
    varRealY = varY[::2]  # Real part
    varImgY = varY[1::2]  # Imaginary part

    plt.figure()
    plt.subplot(2, 1, 1)
    plt.semilogy(varX, varRealY)
    plt.title("Complex - Real Part")
    plt.xlabel("X")
    plt.ylabel("Real Part")
    plt.grid(True)

    plt.subplot(2, 1, 2)
    plt.semilogy(varX, varImgY)
    plt.title("Complex - Imaginary Part")
    plt.xlabel("X")
    plt.ylabel("Imaginary Part")
    plt.grid(True)

    plt.tight_layout()
    plt.show()
```

9. You may unregister the DLL after use like so if you don't trust an old dll lying around on your system.

```bat
regsvr32 /u .\DactronSignal.dll
```