Baking System

Baking is an essential and unavoidable process necessary for achieving Ultra High Vacuum. Optimized bake-out procedures are very important for the overall reliability of vacuum system. In this process the UHV components like Sputter ion pump (SIP), Titanium sublimation pump (TSP) along with the vacuum chambers are subjected to baking for sufficiently long period of time, ~60 hrs. INDUS-2 vacuum chambers are made of Aluminum alloys,  which demands very slow and controlled baking.  In order to achieve this, an intelligent ON/OFF control system was designed, incorporating modular baking system, with distributed controls. Later on pressure monitoring was also included in the system.

This system contains Temperature controller unit (TCU), Pressure Monitoring Unit (PMU), as well as Temperature controlling & pressure Monitoring Interface Software (TCPMIS). Each TCU is an eight channel temperature controlling unit. PMU is eight channel pressure monitoring unit to which analog data from gauges like Penning, BA Gauges are fed.

TCPMIS is a user interface software developed for, controlling up to 5 TCU-s. In this way, 40 channel temperature control, data logging of 40 channel temperature and logging of eight channel pressures was realized.

TCU:

Each module unit is having provision of 8 channels. TCU is capable of monitoring as well as controlling the temperature & able to communicate to computer through half-duplex RS485 network. The address of each TCU can be changed by using DIP switch.

K-type of thermocouple is used for measurement of temperature. TCU measurement range of temperature is up to 500ºC, having resolution of 1ºC. Module is able to handle grounded as well as ungrounded thermocouple. Provision is kept for open sensor detection as well as input voltage protection up to 75V.

In input section differential as well as common mode RC filter is used.

The input amplifier is instrumentation amplifier AD620 which is having CMRR   of 100dB at the gain of 10.

The ADC is AD574, 12 bit; successive approximation is preferred because of multiplexing of 8 channels, compact size, and minimum external components. The controller is 89c52, which is avoiding the need for external ROM & RAM.

Each channel is having SSR (Solid state Relay-Zero crossing) which can give ON/OFF type of control to heaters (up to 2 kW). These relays can be controlled remotely as well by using switches provided on unit’s front panel. Heat sink and cooling fan provision is made for reliable operation of SSR

TCU

PMU:

During and after completing the bake-out, pressure in the system has to be monitored continuously by using Penning Gauge and BA Gauge.

These gauge controllers provide logarithmic 0-10V signal. This signal is used for data logging of pressure readings by using PMU. Each PMU can monitor pressure of 8 channels. These units also support  RS485 communication.  PMU converts analog data to digital count by multiplexing the 8channels and using, 12 bit, successive approximation ADC, 89c51 micro-controller. It transmits data over RS485 network whenever asked. This count is converted to pressure in the computer software TCPMIS.

PMU

Temperature controller & pressure monitoring interface software (TCPMIS):

Graphical user interfacing software TCPMIS has been developed for this entire system by using Visual Basic. By using this software temperature of 40 channels and pressure of 8 channels can be monitored. SET POINT is the required temperature value at controlling point, can be entered by user for each channel. The temperature data can be logged in EXCEL FILE format. Fifteen modules of TCU, three of PMU have been developed and extensively used during the baking of all UHV components, used for INDUS-2, in their vacuum qualifying tests. Total baking procedure was satisfactory and reliable.

TCU Unit with TCPMIS

Temperature Monitoring unit (TMU):

In INDUS-2 along the ring around 148 channels temperature is to be monitored at different points as photon absorbers, dipole chambers, straight sections etc.

For this purpose temperature monitoring unit (TMU) is developed. Its most of the features are same as of TCU with some changes as per needed excluding the part of controlling the temperature.

In one sector among the four, system will be capable of monitoring 40 channels. Total 20 TMU-s will be used which are capable of monitoring temperature of 160channels.

There will be two set points as Alarm set point & Trip set point. Both set points can be changed remotely.

TMU