With the exception of process control vibration transmitters (LPS), most Wilcoxon Research® industrial sensors require an industry standard constant current DC power source. Generally, the power supply contains an 18-30 volt source with a 2 -10 mA constant current diode (CCD).
AC coupling and the DC bias voltage
Whether an accelerometer or piezovelocity transducer (PVT), the sensor output is an AC signal which represents the physical vibration occurring where the sensor is mounted. This AC signal is superimposed on a DC bias voltage (also referred to as bias output voltage or BOV). The DC bias voltage must be removed so that the AC vibration signal oscillates positive and negative about 0 volts. Removal of the DC bias is usually accomplished with a blocking capacitor, which passes the AC output signal to the acquisition system. Most monitors and sensor power supply units contain this blocking capacitor for AC coupling. If not included, a blocking capacitor must be field installed.
Amplitude range and the supply voltage
All Wilcoxon Research® accelerometers and velocity sensors have a preset DC bias output. Ideally the BOV is halfway between the lower and upper cutoff voltages. The difference between the bias and cutoff voltages determines the voltage swing available for the sensor. The available voltage swing and the sensor sensitivity determine the total vibration amplitude range. Thus, an accelerometer with a sensitivity of 100 mV/g and a peak output swing of 5 volts will have an amplitude range of 50 g peak.
Note: A supply voltage of 24 VDC or greater may extend the amplitude range to 100 g peak. If a voltage source lower than 18 volts is used, the amplitude range will be lowered accordingly. Custom bias voltages are available for lower or higher voltage supply applications. Also, high temperatures (>200º F) can reduce the acceleration range.
Constant current diodes
Constant current diodes (CCD) are required for nearly all industrial accelerometers and PVT sensors. In most cases, they are included in the companion power unit or data acquisition system. Generally, battery powered data collectors contain a 2 mA CCD to ensure long battery life. Line powered acquisition systems (where power consumption is not a concern) often contain 6 -10 mA CCDs for driving long cables. For operation above 212º F (100º C), where amplifier heat dissipation is a factor, limit the current to less than 6 mA. If the power supply does not contain a CCD for sensor powering, one should be placed in series with the voltage output of the supply.
Note: Ensure that proper diode polarity is observed!
Click on the product name for description or on the PDF icon for a spec sheet.
(*) indicates models most commonly used by industry.
|CC701 In-line charge converter *||Constant current powered, 1 mV/pC|
|CC701A In-line charge converter||Constant current powered, 10 mV/pC|
|CC701HT In-line charge converter||Constant current powered, 4 mV/pC, compatible with high-temp sensor 376|
|CC726E In-line charge converter||Constant current powered, 4 mV/pC, certified Intrinsically Safe, compatible with high-temp sensor 376E|
|LA704B Line adapter *||120 VAC, used with P702B, P703B and P704B power units|
|LA704B-220 Line adapter||220 VAC, used with P703B and P704B power units|
|NC3 NiCad battery kit||3 rechargeable NiCad batteries & LA704 charger, recommended option for P702B, P703B and P704B power units|
|P31 Power unit/amplifer||Ultra low noise, used with 731A seismic accelerometer, battery powered gain of 1, 10, 100, selectable velocity conversion, internal constant current sensor power|
|P702B Power unit/amplifier *||General purpose, battery powered gain of 1, 10, 100, selectable velocity conversion, internal constant current sensor power|
|P703B Three channel power unit *||Battery powered, constant current source, AC coupled output|
|P703BT Three channel power unit||Battery powered, constant current source, AC coupled output, for use with triaxial sensors|
|P704B One channel power unit||Battery powered, constant current source, AC coupled output|
|PR710A Ten channel power unit/amplifier||110 VAC, gain of 1,10, or 100, selectable filtering or velocity conversion, 19" rack|
|PR710B Ten channel power unit/amplifier||110 VAC, gain of 1,10, or 100, selectable filtering or velocity conversion, 19" rack, twin axial BNC inputs|