All supported configurations for cryogenic and furnace controllers as well as the superconducting magnets are now predefined and the user selects one from the displayed lists. The selected configuration is volatile i.e., ICP does not remember it if the program is exited and then started again. The current temperature and/or magnetic control device must be redeclared every time ICP is restarted. No access to these devices is possible until the TDEV (for temperature) and HDEV (for magnetic field) commands have been executed. If a device is changed without exiting ICP, the appropriate command must be reentered. To find out about the current settings type PTD and/or PHD and ICP will print out the currently used configuration. To use a temperature controller in any way, the T+ flag must also be set. To use a magnetic field controller in any way, the H+ flag must be set.
Controlling temperature during scans is easy to do in ICP. However, remember that the T flag must be set to T+ before a buffer is executed, or the temperature fields in the buffer are ignored.
For the experimenter's convenience several fields are provided in the buffers for controlling the temperature. See Figure 3. There is the temperature-start field marking the starting point of a temperature scan or just a fixed temperature at which the buffer should run. It should be noted that a value of 0 for this field is a special flag to ICP. The temperature is not set or changed during a buffer execution if this ``temperature start'' field is set to 0. The temperature-increment field is used to specify the amount the temperature is to be changed at each point. This value should be zero for BT-1, so that the temperature is set to the ``temperature start'' value at the beginning of the buffer execution and not changed again for the remainder of the buffer. The Wait and the Err field are useful in specifying how long to wait for the temperature to reach its new target. Every time the temperature is changed, the system will pause the data acquisition until either the temperature is within the error specified by the Err field or until the wait time exceeds the maximum wait given in the Wait field.
The two hold fields in each buffer allow the user to define constant wait times to be executed in the buffer's scan. Because these waits are designed to allow the sample environment to stabilize, they will be ignored unless either the T+ flag or the H+ flag is set. The Hld0 field indicates how long the system is to be paused once and only once at the very beginning of a scan (most commonly for use after the temperature and/or field have been set to their initial values). This feature is useful when running scans at a constant but different temperature, enabling the newly set temperature to stabilize. The value in the Hld field indicates how long the system should pause at each point in the scan, and should be zero for BT-1 data. ICP also supports a HOLD command which can be entered in Control Mode or included in Run Sequences and Run Sequence Files to cause a HOLD between buffers. Once the system goes into a wait state a ***HOLD*** message is shown in the status line; the HOLD can be terminated by hitting CTRL-A once (hitting CTRL-A a second time causes the run to be aborted).
In order to get a temperature reading every time intensity data are written, set the temperature flag to T+. Remember, the temperature fields in the parameter buffers also become active when this flag is set to T+ unless the Starting Temp Field is zero.
The temperature can be read and changed from Control Mode using the commands listed below. TDEV must be executed and the T+ flag must be set for temperature.