Instructions for SONIC temperature controller - 1993/03/10 The temperature control system consists of three elements: the dewar, the model DRC-91 controller, and an external computer. Cooling is provided by a refrigerator which runs at full power all the time. The refrigerator has two stages. The first reaches a temperature of about 50 K and is used to cool the shield. The second stage reaches about 10 K and is used to cool the detector. A heater is used to control the actual operating temperature. Heater power is controlled by the DRC-91. A problem with the refrigerator is that the cooling power varies slightly on time scales of a few seconds. Unless this were somehow corrected, the temperature of the detector would also vary. The variations are eliminated by attaching the cooler to a control stage, on which are also located the heater and a thermometer. This thermometer is monitored by the DRC-91, which keeps the temperature of the control stage constant. The control stage is connected to the detector block through a constant thermal resistance. If all else were constant, the detector block would maintain constant temperature. In practice, variations in outside temperature can affect the temperature of the shield and indirectly that of the detector block. Also, reading out the detector deposits significant power in the detector block, and especially for frame times shorter than one second, the detector temperature will increase as the frame time is made shorter. Fortunately these changes have long time constants and can be compensated by an external computer. The temperature controller is capable of monitoring up to six thermometers and varying power to a heater to hold one channel to a constant temperature. Only four thermometers are used in the SONIC as shown in the table below. (Only three channels are used while observing. Channel A3 will mess up your data!) The channels are designated differently in the computer than on the controller. SONIC TEMPERATURE CHANNELS DRC-91 Computer Use Normal channel channel Temp. B 1 Control Stage 25.7 K A 2 not used A1 3 not used A2 4 Detector Block 30.0 K A3 5 Detector 0 volts (off) A4 6 Shield 50 K The controller can be used without the computer to monitor any channel desired. Channels should NOT be changed manually when the computer is running, however. Instead, look at the log file on the computer or at the instrument status display. To select channel B for monitoring, push the "B" button in the upper left corner of the controller. To select any A channel, push the "A" button. Pushing the button repeatedly cycles through all the A channels, and the display shows which is being monitored. The display units can be changed by the button just below button "B" and are indicated by lights at the bottom. In operation, the controller tries to vary heater power to keep channel B at a constant temperature. The temperature "setpoint" is shown at the bottom of the display and can be changed with the buttons below the display. Setpoint units can also be changed but should always be kelvin (K). Typical setpoints are around 26 K, but they will vary depending on dome temperature and other factors. When the computer is operating, it varies the setpoint in order to maintain constant the temperature of channel A2. Computer operation is discussed below. The controller algorithm for keeping the channel B temperature constant is set by the three knobs to the right of the controller. These should be set to the positions marked around the dials. There should be no reason to change these settings. Incorrect settings will cause the temperature to oscillate or not to be properly controlled at the setpoint. The buttons below the knobs set the heater power range. The controller should be set on range "-2", and normally the power, indicated in the display above the knobs, will be around 60%. The local/remote buttons control whether the control algorithm is set by the knobs or by the computer; normally it should be left in "local." The computer program to interact with the DRC-91 is called "irtemptrol" and resides in the /Realtime/bin directory. Depending on the arguments with which it is called, the program reads out the temperatures of all six channels, stores the results in a log file, and varies the channel B setpoint in order to maintain the temperature of channel A2 as nearly constant as possible. The program also puts the measured temperatures into shared memory so they can appear in the instrument status display and be stored in the headers of the data files. The channels are labelled differently in the computer than on the controller as shown in the table above. Normally the irtemptrol program is started with a shell script "tsonic." The script, together with defaults, tells irtemptrol to maintain channel 4 at 30.0 K and to log once per minute in a file called "temp.log" in the current data directory. Once the log file is opened, the program will continue using the same file, so to get the log into the correct data directory it is necessary to run the tsonic script at the start of each night. The tsonic script should kill any irtemptrol process that might already be running. To kill an irtemptrol process without starting a new one, use the script "killirholdtemp". The script "tsonic" takes up to two arguments, though these should seldom be necessary. The first is an optional "-n", which would tell the program to make a log file but not to vary the temperature setpoint. This might be used to monitor a cooldown or warmup. If the "-n" argument is used, any other arguments are ignored. If no "-n" appears, the first argument is the temperature to which channel 4 will be maintained. The second is the setpoint to be used for channel 1; the controller will immediately be commanded to that setpoint, and the program will vary the setpoint from there in attempting to maintain the channel 4 temperature. If more flexibility is needed, irtemptrol can be started directly. Type "irtemptrol -help" to get a list of arguments. Power Failures If the power goes off, the cooler shuts down. The temperature controller should be plugged into UPS power and keep running. Even so, there will be a temperature variation of a few tenths of a degree, depending on how long the power failure lasts. Data taking should stop (if you want reliable data) until the temperature is stable again. It may help to restart tsonic specifying a setpoint, as mentioned above. Controller Wiring From the dewar, four thermometer lines and the heater line must go to the controller. Three thermometer lines go through the bias cable, the smaller of the two cables to the dewar. The shield thermometer goes through the clock cable. The heater line is the twisted pair attached to the clock cable. It terminates in a four pin plug; contacts A (the big one) and B are the heater. The heater is a 100 ohm resistor; with the wiring, the resistance measured externally should be around 105 ohms. In operation, the four thermometer lines go from the camera electronics to the controller via a 9-pin D-connector. The other end of the cable goes to a special compact connector on the back of the DRC-91. The heater goes to binding posts on the back of the DRC-91 through a 16-gauge two-conductor cable. The DRC-91 is connected to the computer through an RS-232 link that terminates in a 25-pin cable on the back of the DRC-91. Power for the DRC-91 should come from a UPS outlet. It is also possible to connect the DRC-91 to the dewar without using the camera electronics. There is a set of three connectors wired together: a round one, a D-9, and a D-15. Plug the normal bias cable (the smaller cable with the heater leads) into the dewar, the D-15 into the other end of the bias cable, the round connector into the clock connector on the dewar, and the D-9 into the cable from the controller. In this configuration, all thermometers should function normally. The heater can be plugged into the controller or into an external power supply; the latter is needed for cooling the dewar. Controller Operation Once the controller is hooked up, the only operation needed should be to turn it on and set the "heater range" to "-2". Check that the setpoint is reasonable, usually around 26 K and that the knobs are in the marked positions. If the detector is completely cold, heater power should rise rapidly to 100%, then gradually fall. Meanwhile, temperature B should rise to something above the setpoint, then start to fall as heater power drops. After a few oscillations - perhaps 5 minutes - the channel B temperature should stabilize at the setpoint and the power will be about 65%. Sometimes the controller gets locked up and cannot communicate with the computer; "tsonic" will give a message like "irtscan error." This happens if, for example, two separate irtemptrol programs are running at once. The cause can be verified by pushing any button on the front panel of the controller. (Local/remote is a good choice, or change the setpoint by 0.01D _K.) If the button does nothing, you have found the problem. If this happens, turn the controller power off and back on. The heater range should still be at "-2" when the controller comes back on, but the power will have dropped to zero. The power should quickly rise, and the temperature should stabilize as above. This will destabilize the temperature, of course, and generally the best thing to do is wait 5 minutes or so before trying tsonic again. If the front panel button works, there is some other problem in the communication between the controller and the computer.