CALL   021 29563051

Vibrasindo

provide professional services in the diagnosis and monitoring system with the totality of the machines and realialibility data

Dual Output (Acceleration + Temperature) Sensors

 

QUESTION

Can I use dual output sensors (Acceleration + Temperature) with the vbOnline device?

BACKGROUND
Most accelerometer manufacturers provide some sensor versions which have integral temperature measurement. They typically have a three-pin connector instead of two-pin, with the temperature output on the extra pin and the signal return shared for both outputs. The temperature is output as a DC voltage, with the industry standard sensitivity being 10mV/degC (5.556 mV/degF).

In some sensors the temperature component is powered by the vibration component. In others it is independent, requiring its own ICP-type drive current. The latter type has outputs scaled in degrees Kelvin instead of Celsius.

ANSWER

Yes, the Kelvin/ICP type sensors work very well with the vbOnline device. Typically, 'Average Value' measurements will be scheduled to be taken at regular intervals, with alarm levels applied as required.

The type of sensors in which the temperature part is powered by the acceleration part should NOT be used for two reasons:

  1. The readings tend to be offset (too high) due to impedance miss-matching between the sensor output and the vbOnline device input.
  2. Normal scheduled 'Average Value' measurements cannot be taken as the temperature component of the sensor will not be powered (a work-around is possible by using QuickScan and ensuring that the vibration and temperature signals are connected into adjacent channels of the vbOnline device).


Kelvin/ICP type sensors which are known to be compatible are:

  • CTC TA172-1A (top exit)
  • CTC TA174-1A, TA178-1A (side exit)
  • Wilcoxon 793T-3 (top exit)
  • Wilcoxon 797T-1 (side exit)


To configure Kelvin/ICP type sensors in the Ascent software, set up the sensor as:

  • Sensor Type: Temperature (mV/degC)
  • Input range & coupling: DC -10...10 V
  • Sensitivity: 10 mV/degC
  • DC Offset: - 273 degC
  • Settling Time: 3 s
  • Enable drive current: On


For an output in Fahrenheit, make these changes:

  • Sensor Type: Temperature (mV/degF)
  • Sensitivity: 5.556 mV/degF
  • DC Offset: - 459.4 degF


Note that the output signal of 10 mV/C is very small for measurement by the vbOnline device's DC inputs with their 20 V ranges. The absolute accuracy of the combined sensor output + vbOnline input will be approximately +/- 5 degC. That may not be high precision, but the readings will be very consistent and trendable. Furthermore, with these Kelvin/ICP type sensors, a simple correction to the DC Offset can be applied with confidence.