Frequently asked questions

PI Temperature Controller

The ‘PI Temperature Controller’ double-width SIM (small instrument module) is a temperature-controlling servomechanism designed for use with the special FET-based baseplate-heater system in the TeachSpin variable-temperature cryostat. It requires power from a SIM ‘crate’ or equivalent, and also an external d.c. power supply (capable of up to 60 V, and 1 A) connected at the red(= +) and black (= -) banana jacks on the SIM’s rear panel.

Operation requires the use of the diode temperature transducer on the dewar’s baseplate, and the SIM generates a 10-μA constant current to excite this transducer. The SIM’s front-panel Temperature BNC connector provides an output voltage ten times the voltage drop across this diode thermometer (hence yielding about 4.5 V at room temperature, and about 9.9 V at 77 K).

The SIM compares this 10´diode voltage with a setpoint voltage chosen, in the 0-10 V range, by a 10-turn dial on the SIM’s front panel. The difference yields an ‘error signal’ which can be monitored at the front-panel Error BNC connector. The servomechanism uses a PI, or proportional+integral, algorithm to turn this error signal into a control signal for the FET/resistor heater inside the dewar. The ‘proportional gain’ is set via a 1-turn 0-10 dial, and a x100/x1/x10 toggle switch on the front panel. The ‘integral gain’ is set via a time-constant selected by another 1-turn 1-11 s dial, and another toggle switch for multiplication by 4, 1, or 0.

Connections to the dewar are made via a back-panel 9-pin D-sub connector to a properly-wired Cryostat Interface box, and the connection of that box to the dewar’s 10-wire cable.

The manual for the PI Temperature Controller SIM can be found here.

Current Source

The ‘Current Source’ SIM (small instrument module) can deliver a current of chosen size and sign to a load connected at its front-panel Current Output banana connections.

The current can be chosen by decades in the range 1.00 μA to 100 mA, via the front-panel rotary switch. A toggle switch disables the current, or selects its sign: choice + sends conventional current out of the red banana connector, to return via the black.

Another toggle switch, if set to Local, enables front-panel control of the SIM’s functions; when set to Remote mode, the on vs. off function, and the sign of the current, can be controlled electronically via the rear panel.

Front-panel 2-mm tip-jacks labelled Compliance Monitor permit a monitor of the constant-current function. If, and only if, the chosen current is passing through the load, a potential-difference of 1.000 V will be visible here. If the supply lacks the compliance needed to drive the chosen current though the load, the Fault LED will light, and the monitor voltage will drop below 1 V.

The rear panel’s upper D-sub connector provides ground potential at Pin 5, and a +5-V supply at Pin 3. In the Remote mode, logic high at Pin 1 selects current On (while logic low selects Off), and logic high at Pin 2 selects - sign for the current delivered (while logic low selects +).

The manual for the Current Source SIM can be found here.

Hartshorn Coil-Driver

The ‘Coil Driver’ SIM (small instrument module) maps an a.c. audio-frequency voltage waveform into an a.c. current waveform passing through a floating load. It accepts, at the front-panel Osc. In connector, a voltage signal in the frequency range 50-5000 Hz. Its output current flows between the rear-panel TO COIL plugs. The output current is given by iout(t) = Vin(t)/(10 W), with about 10 V of voltage compliance, for currents under ±220 mA.

The front-panel connector labelled Curr. Mon. is a voltage surrogate for the output current actually flowing, given by Vmon = iout x 1Ω.

The module also makes available, as a low-level voltage at the rear-panel BALANCE OUT connector, an attenuated and modified copy of the current waveform, with full control over the amplitudes of both quadratures of the a.c. signal. To use this output, set the rotary switch to a frequency band including the Osc. In signal frequency, and set the toggle switch to a desired attenuation (÷1, ÷10, ÷100). The knobs I and Q then control the sign and amplitude of the In-phase and Quadrature components of the composite signal emerging at the rear-panel output.

The manual for the Hartshorn Coil-Driver SIM can be found here.

Dual Current Source

The ‘Dual Current Source’ SIM (small instrument module) contains a pair of 1/10/100 mA current sources, and each will deliver the selected current to a load connected at its rear-panel Current Output BNC connector.

The ‘A’ and ‘B’ sections of the SIM are independent, but of identical construction. Each section has a three-way toggle switch, allowing the selection of 10/1/100 μA output current. The currents are positive-only, with conventional current leaving the back-panel BNC by the center pin, and returning to the shell (at ground potential). Note that thereby the external load has its current-output connection held at ground potential.

Each section has a front-panel monitor-voltage BNC connector, and at this connector there appears a (positive) ground-referenced potential difference given by Vmon = Iout x 5 kΩ. Hence if the output current successfully reaches 1, 10, or 100 μA, there should appear here a potential difference of 5, 50, or 500 mV.

The voltage compliance of the current supplies is >10 V, implying that the supplies can drive a full 100-mA current through a load of resistance up to 100 kΩ (developing an output voltage of ΔV = I R = 100 μA x100 kΩ = 10⁻⁴ A x 10⁵ Ω = 10 V to do so).

The manual for the Dual Current Source SIM can be found here.

High-Gain Utility Amplifier

The ‘High-Gain Utility Amplifier’ double-width SIM (small instrument module) will amplify steady and low-frequency signals by a gain up to 10⁶, and offers adjustable d.c.-offset and time-constant adjustments.

The inputs are differential-mode; the + and – input BNC connectors can be set to ground, or to 10-MΩ or to much higher input impedance. Input Gain selects the factor (in the range 1 to 1000) by which the difference V+ - V- will amplified. The amplified difference appears as a ground-referenced voltage at the BNC connector Monitor.

The output of this first-stage amplifier will be time-averaged by a one-pole filter with the Time Constant chosen (in the range 0.03 s to 10 s). To that time-averaged result you may apply a zero-offset (of either sign, and of magnitude up to 10 V), set by the DC Offset 10-turn dial.

Finally Second-Stage Gain sets the factor (in the range 1 to 1000) by which the resulting averaged and dc-offset signal will be further amplified. The result appears as a ground-referenced voltage at the BNC connector Output.

The manual for the High-Gain Utility Amplifier SIM can be found here.

Pulse Current

The ‘Pulse Current’ SIM (small instrument module) delivers a stabilized current to a floating external resistive load for a specified time, while permitting a monitor of the potential difference arising across the load.

The uppermost knob selects the pulse duration, from ¼ s to 128 s, in power-of-2 steps. The knob below it selects the current sent to the load, with choices in the 20 mA to 320 mA range. The toggle switch may be set to Ext Trig to deliver one pulse per rear-panel electronic command, or it may be manually spring-depressed once to the On position to deliver a single current-pulse. Raising that toggle switch to the upper CW position instead results in a continuous (un-pulsed) steady output current.

The front-panel connector labelled Voltage Monitor delivers a buffered and ground-referenced copy of the potential difference developed across the external load.

The rear-panel upper D-sub connector permits connections to the load. Pins 4 and 5 of this connector (labelled I+ and I-) are for the supply, and the return, of the specified current. Pins 8 and 9 (labelled R+ and R-) are for two additional potential-monitoring wires attached ( in 4-wire fashion) to the load. Pin 2 accepts a rising 0→+5 V edge for use in the external-trigger mode. Pin 3 is a rear-panel copy of the front-panel voltage monitor; it’s a ground-referenced voltage output of the potential difference across the load.

The manual for the Pulse Current SIM can be found here.

High Tc Superconductivity

The ‘High Tc Superconductivity’ SIM (small instrument module) is devised to support the use of the temperature-regulated Hall sensor that’s used in the Persistent-Current experiments in CMP-SC.

The left-hand section processes the signal from the Hall-effect field sensor. To the raw sensor output can be applied a Gain (´1, 2, or 10) and a double-pole low-pass filter of Time-Constant 0.1, 1, or 3 seconds. To that result may be applied a d.c. Offset, set to positive, negative, or OFF functions by toggle switch, and adjustable in the 0 – 10-V range by 10-turn dial.

The right-hand section provides for thermal stabilization of the Hall sensors, via a P/I servo-controller using a resistive heater. The SIM provides a 10-mA constant-current source to a diode that senses the temperature of the probe; that diode voltage, typically in the 0.45 – 0.99-Volt range, is amplified 10-fold, and compared with set-point established in the 0 – 10-V range via the 10-turn dial. An LED shines red or green if the actual temperature departs from the set-point, and goes out when the error signal has been driven to zero.

The rear panel’s upper D-sub connector provides connections to the field-sensor unit: I+ and I- provide the current to, and return the voltage from, the temperature sensor; Heater+ and Heater- are the resistor connections; Signal+ and Signal- are the raw hall-sensor outputs; +5 V is the supply to the Hall sensor itself, and GND is ground potential. Pin 8 is unused.

The manual for the High Tc Superconductivity SIM can be found here.

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