EL3632 — Vibration Acceleration Calculation

 

EL3632 — Vibration Acceleration Calculation

Module note (excitation current):
The EL3632 measurement module provides selectable excitation currents of 2 / 4 / 8 mA. When the sensor cable is relatively long, select 8 mA to ensure reliable sensor excitation.

Spectrum vertical-axis units

The vertical axis of the spectrum is related to the sensor parameters (chiefly the sensor sensitivity).
If the spectrum amplitude is given in raw ADC counts (YA), you must convert counts → voltage → acceleration (g) → acceleration (m/s²) using the sensor sensitivity.

Conversion formula (counts → g → m/s²)

1. Counts → Voltage

   Let

   • YA = measured amplitude in ADC counts (unitless)

   • Vref = ADC reference voltage (for EL3632 example, 5 V corresponds to full-scale)

   • ADC_fullscale = full-scale ADC code (use 32768 for a 16-bit signed range representation; EL3632 max positive value is 32767)

   Voltage corresponding to YA:

   $$V = YA \times \frac{V_{ref}}{ADC_{fullscale}}$$

2. Voltage → acceleration in g

   Let S = sensor sensitivity in V/g (for many accelerometers sensitivity is given as mV/g; convert to V/g by dividing by 1000).

   Acceleration in g:

   $$a_{(g)} = \frac{V}{S} = YA \times \frac{V_{ref}}{ADC_{fullscale} \times S}$$

3. Acceleration in m/s²

   Use gravitational constant g = 9.81\ \text{m/s}^2:

   $$a_{(m/s^2)} = a_{(g)} \times 9.81$$

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Worked example (your numbers)

• Sensor sensitivity $S = 100\ \text{mV/g} = 0.1\ \text{V/g}$

• Measured spectrum amplitude $YA = 3000$ (ADC counts)

• $V_{ref} = 5\ \text{V}$

• $ADC_{fullscale} = 32768$

Step-by-step:

1. Numerator: $YA \times V_{ref} = 3000 \times 5 = 15000.$

2. Denominator: $ADC_{fullscale} \times S = 32768 \times 0.1 = 3276.8.$

3. Acceleration in g:

   $$a_{(g)} = \frac{15000}{3276.8} = 4.57763671875\ \text{g}$$

   (rounded to two decimal places: 4.58 g)

4. Convert to m/s²:

   $$a_{(m/s^2)} = 4.57763671875 \times 9.81 = 44.9066162109375\ \text{m/s}^2$$

   (rounded to two decimal places: 44.91 m/s²)

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Notes on maximum measurable frequency

The maximum measurable frequency is limited by the sampling rate. In a PLC context the effective sampling rate depends on:

• the PLC task cycle period (T_task), and

• the oversampling count (N_os) used inside that task (if the module or your code performs oversampling per task cycle).

A simple estimate:

• Effective sampling frequency:

  $$f_s = \frac{N_{os}}{T_{task}}$$

  (e.g., if T_task = 1\ \text{ms} → $1/T_{task} = 1000\ \text{Hz}$; with N_os = 4 → $f_s = 4000\ \text{Hz}$.)

• Nyquist maximum measurable frequency (single-sided):

  $$f_{max} \approx \frac{f_s}{2}$$

  (In the example above $f_{max} ≈ 2000\ \text{Hz}$.)

Important: the exact maximum useful frequency depends also on EL3632’s internal sampling/decimation behavior, anti-alias filtering, and how you configure oversampling/decimation in the module or PLC. Always verify with:

• the EL3632 datasheet / manual for the module’s native sample rate and filter settings, and

• the PLC task/scan configuration and any software oversampling you apply.

  

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Practical reminders / best practices

• Use the highest practical excitation current (8 mA) for long sensor cables to preserve signal amplitude at the sensor.

• Confirm the ADC reference and full-scale mapping in your specific EL3632 firmware version (EL3632 maps ± full-scale to ±32767 in many Beckhoff implementations).
  

• Prefer storing spectrum amplitudes as physical units (m/s²) in post-processing or HMI display — convert counts to physical units as shown above before analysis.

• Check anti-alias filters and sampling chain when you push toward high-frequency measurements.