When an IEPE (ICP) Sensor is activated, the initial 24 volt supply has to 'settle' for a prescribed period before the sensor is ready to operate. During this period of settling, measurements made with the sensor could provide inaccurate data, especially in the low frequencies. 

Issues with ICP Settling can present as: 

• Poor selfcheck data
• Poor coherence in the low frequencies after selfcheck
• High calculated displacement in shock testing
• Distorted time-domain measurements or FFT
• In Random testing: Poorly controlled lower frequency data in the beginning of a test that take a long time to correct. 

Instructions to correct issues related to settling time

Step 1: Determine the settling time of your sensor

• Once the channels for ICP sensors are configured in VibEdit, open the setup file in VibRunner, without selecting Selfcheck
• Select the Scope Mode button and immediately select Start TP  and select OK in the pop-up window. 
• Optional: Configure a plot window to display one or more channels containing IEPE sensors in the Time Domain
  • Double click on any plot window
  • Set the Master/Secondary channels as channels you are interested in (IEPE)
  • Select Time Domain as the X-Axis data type
• After the throughput has recorded for an ample ammount of time (Typically < 1 minute for accelerometers and < 3 minutes for prepolarized microphones) select the Stop TP button. 
• Selct the VibPostTest Button
• Select the channels of interest in VibPostTest and note the point in time where the measurement settles, or begins to remain at zero. In the example below, this occurs at around 10 seconds. 
• Make sure to record the longest settling time of the group for the next step.

Scope Mode/TP Control Window in VibRunner:

Setting the Plot Display to show Time Domain:

Shortcut to VibPostTest:

ICP Settling in the Time Domain: 

Step 2: Change the Default ICP Settling Time

• Open the vcpnt.ini file in the directory C:/VcpNT/Config/Users/[username]
• Using CTRL+F, search for "ICP"
• Set the line ICPWaidTime to the desired duration 
• Save and close the file. 

In the example above, the string would read:

    ICPWaitTime=10

OR

Step 3: Alternatively, set ICP to Stay On

• To keep the IEPE circuit on after the initial selfcheck, change the ICPKeepOn to the desired setting as shown below

ICPKeepOn=1

Note the defaults for these settings:
    ICPWaitTime=5
    ICPKeepOn=0
Where 0 = Off and 1 = ON