Drive Current

We connect the drive circuit inputs with a 1.993 kohm resistor and measure the drive current for both a DC and demodulated 6 Hz sine wave signal. Each plot includes the 20 second timestream, the timestream psd, and the timestream psd in machine units.

Figure 1 A 0 amplitude DC signal

Figure 2 A 6 Hz signal with 23.1nA current (not demodulated)

Figure 3 A 6 Hz sinewave with 23.1nA rms current (demodulated)

Sense Current

We connect the sense circuit inputs with a 1.998 kohm resistor and measure the voltage output (isolated from the drive current). The plot includes the 20 second timestream, the timestream psd, and the timestream psd in machine units. The dashed green line is the voltage noise prediction from the combined Johnson noise in the resistor and the amplifier white noise level (added in quadrature).

Figure 4

Resistance Measurement

We connect a 1.993 kohm resistor across the sense and drive circuit inputs. The green dashed line in the resistance plot is the noise prediction due to the voltage noise only.

DC bias
Figure 5 Current Measurement

Figure 6 Voltage Measurement

Figure 7 Resistance Measurement

6 Hz sinewave bias
The signal is modulated to DC and 12 Hz, and the 6 Hz spike is the modulated DC offset.
Figure 8 Current Measurement

Figure 9 Voltage Measurement

Figure 10 Resistance Measurement

17 Hz sinewave bias
The 8 Hz spike is the aliased DC offset that is modulated to 17 Hz, then aliased to 8 Hz.
Figure 11 Current Measurement

Figure 12 Voltage Measurement

Figure 13 Resistance Measurement

RTD Measurements

The following plots are taken from measurements of a cold UC head in the dewar (~2 kohm)
Figure 14 Current Measurement

Figure 15 Voltage Measurement

Figure 16 Resistance Measurement

Script

The script used to generate the above plots is HERE. You will need to change the ip address and port that the script streams to. It includes packages from the pyWTL directories.

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This topic: CryoElectronics > WebHome > CryoNoise Topic revision: r4 - 2010-12-02 - JamesKennedy

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