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SQE-DC- 100
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SQE-DC- 400 k |
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| Our models SQE-DC-100k and SQE-DC-400l are ac-flux modulated dc SQUID
readout circuits with a modulation frequency of 100 kHz and 400 kHz, respectively.
Other modultaion frequencies are available on request. The electronics
features a very-low-noise preamplifier with a noise temperature of less
than 10 K ( typically 4 K for a source impedance of 20 ohms ). Due
to the ac-flux modulation, drift and low-frequency excess noise due to
temperature fluctuations are supressed. The SQUID readout measures
only 94 mm by 57 mm by 35 mm and weighs about 160 g. As it is small
and light, it can be placed close to the SQUID.
This SQUID readout is ideally suited for measurements at lower signal frequencies, such as noise thermometry, gravity-wave or geophysical experiments, or biomagnetic measurements. The SQUID readout circuits are controlled by our control box SQC-1, which can be placed several meters away from the readout. This control box is used to set the bias current of the SQUID, the flux-modulation amplitude, the phase shift between modulation and internal lock-in reference, and the feedback resistor (eight values between 5 kohm and 180 kohm can be selected). The actual parameters are displayed on a illuminated LCD display and can be changed manually, or by a personal computer via the serial port. A personal computer, however, is not required to operate the SQUID readout. The internal microcontroller of the control box can be switched off when performing extremely sensitive measurements. The parameters for 20 different SQUIDs can be stored internally, and can be recalled when the same device is being used the next time. The size of the control box is 165 mm by 110 mm by 40 mm. The box can either be battery operated (at any dc voltage between 18 and 24 volts) or supplied from a mains-operated power supply. The current consumption is about 200 mA (display on), or 100 mA (display off). The SQUID readout is supplied with power from the control box. The SQUID readout can also be supplied with a built-in rechargable battery allowing for a measuring time of 4 to 8 hours (in a larger box, see the picture of our SQE-DC-BR-400k below). |
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SQC-1
SQUID-readout
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| Our dc SQUID readout circuits SQE-DC-100k and SQE-DC-400k are also available with bias-reversal modulation. Bias reversal will suppress low-frequency excess noise produced by critical current fluctuations, and is especially helpful when reading out high-temperature superconductor SQUIDs. 1/f noise produced by critical current fluctuations can also be a problem in LTS SQUIDs when magnetic fields at very low frequencies (mHz) have to be measured. |
| SQE-DC-BR-400k
SQUID readout circuit
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| For applications requiring a large dynamic range at relatively high signal frequencies, we offer SQUID readouts with ac-flux modulation frequencies between 1 MHz and 25 MHz. The standard model is our readout SQE 4 M. It is an ac-flux modulated dc SQUID electronics with a modulation frequency of 4 MHz, which we also employ in our NDE systems. The preamplifier has a noise temperature of less than 15 K (typically 10 K for a source impedance of 20 ohms). The bias current for the SQUID, the preamplifier gain, the modulation amplitude and the phase between modulation and internal lock-in reference can be adjusted. Eight different feedback resistors can be selected. With a good niobium SQUID, a dynamic range of up to ten flux quanta can be achieved at frequencies above 100 kHz. The SQUID readout can be controlled by our control box SQC-1, or our NDE controller WBS LKI 250k. The SQUD readout measures 165 mm by 110 mm by 40 mm. |
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SQE 4 M
dc SQUID readout circuit with 4-MHz modulation frequency. |
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