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To set up Recorder Out, identify the minimum and maximum power levels (in dBm) that you require.
Place these values in the RecorderOutLowerLimit and RecorderOutUpperLimit in the left hand pane as
shown in Figure 1. Once the values are established, the formula below can be used to determine the
output voltage (Vout) for any given dBm power level.
Vout= (10^(PMEAS/10)-10^(ZeroVoltSet/10))/(10^(OneVoltSet/10)-10^(ZeroVoltSet/10))
The same formula (shown below) can be copied and pasted into excel at cell B4. When pasted into cell
B4, the cells listed below will establish the inputs values. All power units are in dBm. Out of range data is
not accounted for.
B1 is the dBm power setting to deliver for 1 Volt
B2 is the dBm power setting to deliver 0 Volts
B3 is the actual input power.
=(10^(B3/10)-10^(B2/10))/(10^(B1/10)-10^(B2/10))
Grounding Note
LB5900 Sensors have solid grounding between the USB shield, USB Common and SMB (Recorder Out)
Common connections. It is important to take ground current into consideration between all connected
equipment. LadyBug Recorder Out resolution specifications are generally (see specification sheet for
exact specification and sensor accuracy data) in the range of 25 micro volts. Small ground currents
caused by power across shielded cables can swamp the measured output voltage if care is not utilized.
For example, many USB cables exhibit shield and common resistance of greater than an ohm. In this
case, with 200 ma current draw from the sensor, there will be 200mv across the sensor USB cable. If the
computer and the device monitoring the Recorder signal share common grounding, this current will be
driven in a loop and may result in a ground offset voltage on the monitoring device as depicted by the "I
loop" shown in Figure 2. This offset voltage may dynamically change as the sensor's current draw
changes and along with other changes in the ground system.
Figure 2 - Ground Management
DOC: Recorder Out Operation – V2.0 April 2016
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