Low-drift controller for Astronomical RV Spectroscopy applications.

A dual-servo temperature controller with up to four temperature channels, <50microK read noise and a 24-hour stability of 1-2mK. Uses ovenized components to minimise temperature coefficients  and improve long-term stability. Characterisation is ongoing. Final product available Q3 2020. Preliminary information below.

Vacuum System

Control System

Preamplifier Oven

Performance

GUI

Front and Rear Panels

Manual

For this application the requirement is to stabilise a Fabry-Perot (FP) cavity to +/-15mK. Since the cavity is open (as opposed to solid glass) the pressure must also be stabilised due to the pressure dependant refractive index of air.

 

The temperature requirements are met with a two-stage nested design. The pressure requirements are met by ensuring the pressure is constantly monitored and  the vacuum maintained by either pumping on a programmed schedule or using a pressure threshold trigger.

 

The basic temperature controller design contains additional peripheral hardware and micro-controller software to ensure a stable environment for the FP cavity.

 

Prototype vacuum system

Vacuum vessel interior

The controller has been designed from the start for maximum long-term stability and high precision. For this application it has been customised to include additional functionality such as Solid State Relay control, a Vacuum Gauge interface and Electrovalve control.

 

Design customisation available, the basic design is highly expandable.

 

The controller is stand-alone but requires connection to a PC for its initial setup.

 

Temperature and servo power data

is logged internally.

Ovenized PCB. Key preamplifier components are located on a thermally-isolated servo controlled section. This renders the controller insensitive to changes in ambient temperature.

Chopper-stabilized zero-drift electronics.  50/60Hz noise rejection filters and additional digital filtering give read noises of <50microKelvin with diode temperature sensors.

Temperature of the controller case over course of 4 days. The case reflects closely the ambient temperature.

Temperature drift in diode temperature sensor channel over same 4 day period. Drift of -1mK demonstrated. Sensor was replaced with a temperature-stabilised reference resistor with the same dynamic resistance as the real diode sensor. Data shows electronic drift in preamplifier only. The stability of the servo loop is still being optimised.

Raw data available as a downloadable CSV file (Excel readable). Alternatively a dedicated Python visualiser is available.

Python GUI. Runs on host PC and communicates with controller via USB2. Allows setting of target temperatures, downloading of temperature-history data manual control of electro-valve and vacuum pump. Full command vocabulary can be entered textually. This allows flexible setup of loop parameters and the automatic modes.

Command Vocabulary

Control-loop design.

Alternate packaging options on request.

Key data available on front panel LCD.