Data acquisition unit (Agilent 34980A) used for temperature measurement. To obtain maximum sensitivity, the unit is used in 2 wire (2W) resistance measurement rather than temperature measurement. Resistance is then converted into temperature by software. An ethernet port is used to communicate with the unit. WARNING: temperatures cannot be measured below 20.9 C, due to the match between RTD resistance range and data acquisition unit range.

Back of the data acquisition unit showing the connections to the thermistors. We use one module (module 34921A with terminal block connector 34921T), which can connect to 40 thermistors. A maximum of 8 modules can be used for this unit.

The locations of the thermistors is as follows:

1       CCD camera
2       Top of PIAA bench, halfway between PIAA M1 and PIAA M2
3       Side rail 1 (middle)
4       PIAA M2 mount
5       Light source (top of XYZ stage)
6       DM support plate
7       Cooling output on bench (next to Camera)
8       Main side rail, below CCD
9       PIAA M1 mount
10      Cooling input on bench (below DM)
11      air outside enclosure (on door panel)
12      DM mount base
13      air inside enclosure
14      Temperature on heat exchanger body   
15      Water temperature at output of heat exchanger
16      Water temperature in reservoir

Temperature control and insulation

Our temperature regulation mostly relies on a water circuit running through the bench, that includes a heat exchanger with five peltier modules, outside the enclosure. The modules are supplied in current by a computer controlled source, and we were thus able to implement a PID loop, using the data from temperature sensors located at the exit of the heat exchanger. Max power sent to Peltier is 57 W (cooling power ~ 17 W, assuming 30% efficiency).

A program permanently performs this regulation, and monitors the temperature of the heat exchanger, the PIAA bench, the water tank, and the air in the clean room, outside the enclosure.

After doubling the thermal insulation of the PIAA bench enclosure, and insulating all the water circuit outside, the performances of the system were the following :

- In steady state, the Peltier modules require 0.21 A = 2.51 W when both the pumps and CCD cameras are on. The heat produced by the pumps can be seen as a 85 mK offset between the temperature in the pipes and the temperature in the tank. Assuming a 30% efficiency, the pumps inject 750 mW into the circulating water.
- Temperature of water exiting heat exchanger stabilized to 1 mK RMS
- Temperature of PIAA bench oscillating by only +/- 8 mK during 24 hours (because of air conditionning variability in the room), whereas outside air temperature variations are about +/- 1 K.
- Temperature of PIAA bench stabilized to ~2 mK RMS during 6 hours long periods.