Measuring the Channel Voltage

The information provided is for help with Commtest Instruments products:

• vbOnline system

QUESTION

Is it possible to measure the bias voltages of the sensors connected to our vbOnline instrument? We'd like to monitor and trend this 12 V level as a check of the sensors and their cabling.

ANSWER

Yes. This process will be automated in a future release but for now you can measure the voltages manually. To do this you will need to temporarily edit the sensor's details in the software so that it measures voltage instead of vibration.

Editing the Sensor

• From the Ascent menu select Edit>Manage>Sensors.
• Select your sensor (this will probably be 'Accel 100mV/g' or similar) and click Edit.
• Change the Sensor Type from Accelerometer to Electro-motive Force mV/Volts (click the Other button and select Electro-motive Force from the list then click OK).

• Set the Sensitivity/Calibration as 1000 mV/Volts.
• Set the Voltage Range and Coupling to DC 0...20 V.
• Leave the 'Enable drive current' box checked. Leave the other fields at their default values then click OK and Close.

Create a new Average Value Schedule Entry

• Add a new Average Value schedule entry at a measurement location which uses this sensor (right-click the location and select New>Average Value Schedule Entry).
• Enter a meaningful description such as 'Accel Bias Voltage'.
• To take a recording right-click the schedule entry and select Record now using vbOnline. Repeat this for each measurement location (i.e. for each vbOnline channel). If you do this periodically you can trend the value as shown below (this image shows a sensor that has developed a short circuit).

• Once you've collected your recordings you must change the sensor's details back to their original values by working through the above steps again (Edit>Manage>Sensors etc).

An alternative technique is to create a new sensor called, say, 'Accel Bias' and apply the voltage settings to it. If you do this you can avoid changing the details of your main sensor. However, you must then assign this sensor to every channel you wish to measure then change the channel assignments back afterwards.

FAQ ID: 16343 Last Reviewed: 24/11/2005