5.1 Introduction to the IPC Calibration

After the fabrication and testing of each of the four flight model imaging proportional counters (IPCs) was finished at Metorex, the IPCs were shipped to Columbia University for calibration. When the calibration of an IPC was completed at Columbia University, it was sent to SNL for integration into the SXRP flight model. Table 10 shows the dates when each IPC arrived at Columbia University from Metorex and was shipped to SNL from Columbia University.

Table 10: IPCs at Columbia University

The calibration tests were performed in order to determine the IPC response to known inputs, measure IPC performance, and measure temperature dependencies. The following is a detailed report on the Columbia University calibration including descriptions of the testing setups and data taking procedures, explanation of data analysis methods, presentation of the results, and discussion of the results. The report is divided into the following sections: 5.2 Equipment Used During the Calibration, 5.3 Electronics Calibration and Testing, 5.4 X-Ray Response, 5.5 Position Response, 5.6 Spatial Uniformity of Energy Resolution, Gas Gain, and Efficiency, 5.7 Spark Testing, and 5.8 LE1 "Bright Spot".

5.2 Equipment Used During the Calibration

5.2.1 Electronic Components Used for Signal Processing

Seven analog signals are digitized for each event: "Fast Anode", "Slow Anode", Backanti, Sideanti, Wedge, Strip, and Zee. In Figure 5.2-1, a schematic of the signal processing electronics is displayed. After passing through the E-box preamplifiers, the signals coming from the Sideanti, Wedge, Strip, and Zee channels are sent directly to bipolar shaping amplifiers with 8 microsecond time constants, while the signal exiting the Backanti preamplifier is inverted and sent to an identical shaping amplifier. The signal coming from the Anode preamplifier is inverted, and sent to two separate shaping amplifiers. One of the shaping amplifiers is bipolar with an 8 microsecond time constant, while the other is unipolar with a 200 ns time constant. The Slow Anode signal is the output from the bipolar shaping amplifier, and the Fast Anode signal is the output from the unipolar shaping amplifier. The six bipolar signals (Slow Anode, Backanti, Sideanti, Wedge, Strip, and Zee) and the one unipolar signal (Fast Anode) are sent to seven separate linear gates and stretchers. Each linear gate and stretcher is independently triggered. The linear gate and stretcher outputs are then sent to the 12 bit analog to digital converter (ADC) located within the "data acquisition computer" where the digitized signal amplitudes are stored.

Data acquisition is triggered as follows. The Slow Anode signal is sent to a single channel analyzer (SCA), which produces a digital pulse if the input signal has an amplitude between the upper and lower threshold levels. The output of the SCA is inverted using a NAND gate and sent to the ADC trigger input.

The ADC channel assignments for the seven analog channels are shown below.

The following Tennelec components were used to process the IPC signals during the calibration: TC243 - shaping amplifiers for the Slow Anode, Backanti, Sideanti, Wedge, Strip, and Zee electronics channels, TC309 - linear gate and stretcher for the Slow Anode electronics channel, TC310 - linear gates and stretchers for the other electronics channels. A TC253 - Dual Sum and invert module was used as an inverter, and a TC450 - Single Channel Analyzer was used to trigger data acquisition. An Ortec 579 fast filter amplifier was used as the shaping amplifier for the Fast Anode. A Texas Instruments 7400 NAND gate was used as an inverter. For analog to digital conversion, a Data Translation model DT2824-PGH digital input-output and ADC board for IBM AT-compatible computers was used.

5.2.2 Other Devices Connected to the IPCs

Pulsers: Two BNC Model BH-1 Tail Pulse Generators were used to send pulses to the preamplifier test pulse inputs.

Power supplies: Power was provided for the IPC preamplifiers using two Uniply 6050D power supplies. A Trygon electronics SHR 40 supply was used to power the 7400 NAND gate used as an inverter. A low voltage power supply was also used to power the flight model HVPSs. Occasionally, testing of the IPCs required the use of high voltage power supplies other than the flight model HVPSs. In this case, two Bertan model 305 power supplies were used to supply power to the Anode and Anti high voltage electronics chains, and a Bertan model 301 was used to supply power to the Cathode high voltage electronics chain.

Electronic Monitoring and Measurement: A Tennelec TC535P Timer/Multi-Scaler was connected to the output of the SCA to monitor the number of acquired events. A Tektronix 2465 Oscilloscope and a Fluke 8050A Digital Multimeter were used to make various signal and low voltage DC measurements. To make high voltage measurements, Sensitive Research 500 V, 2 kV, and 5 kV electrostatic voltmeters were used.

Computer equipment: Two Dell 433SE computers were used during the calibration. Both contained 486 processors and 1542 Adaptec Host Adapters which allowed for connections to optical disk drives. One of the computers functioned as a data acquisition computer. It contained the ADC board described above. The other computer functioned as a data analysis computer. A Pinnacle Micro RCD-1000 recordable CD-ROM device was also used for data storage. All the data taken during the calibration was saved to both optical disk and CD-ROM.

5.2.3 Software

Software was written to do three main tasks: 1) Acquire data, 2) Control the HVPSs, and 3) Analyze the data. Acquisition software was written in C++ which can be used under either DOS or OS/2. The acquisition software writes data into 2048-byte blocks each of which contains 112 events. The software used to control the HVPSs was also written in C++ and can be used under either DOS or OS/2. The HVPS software controls the number of electrical pulses sent to the power supplies. For each supply, sending 1024 pulses ramps the supply up to full scale (4000 V for the Anode and Anti supplies and 700 V for the Cathode supply).

Two software packages are used to analyze the data. One package, written in C++, is named "look". Look allows the user to produce histograms and "scatter plots" to display the data. During the calibration, look was used as a quick way to check the acquired data. The other software package is called "cart" and is written in IDL and C++. Cart has been used to perform a detailed analysis of the calibration data.

5.2.4 Other Equipment Used for the Calibration

X-Ray Beam Line, Hole Pattern, and Associated Vacuum Equipment: As shown in Figure 5.2-2, the beam line is 3.9 m long from the source anode to the IPC window. At one end is a chamber housing an x-ray source which is usually operated at power levels between 1 and 2 W and between voltages of 10 and 20 kV. A kapton window separates the x-ray source from the central chamber. The central chamber is a stainless steel tube with an inner diameter of approximately 20 cm which extends from the x-ray source to a flange on which the IPC can be mounted. A Varian SD-300 mechanical pump is used to evacuate the central chamber to a pressure below 1 mtorr. For the x-ray source, a Varian Vacsorb sorption pump is used as a roughing pump for a Triode Vacion pump which can evacuate the x-ray source chamber to a pressure below 10-6 torr.

As shown in Figure 5.2-3, the hole pattern consists of an 18 by 16 pattern of 0.5 mm diameter holes with 6.26 mm spacing between holes in both directions. It is mounted on the same flange as the IPC so that the space between the hole pattern and the IPC strong back is small (about 1 cm).

Sealed Radioactive Sources: The radioactive sources 55Fe, 109Cd, and 57Co were used to illuminate the IPCs with x-rays of known energies. The principal decay products emitted from these sources and their corresponding energies are listed in Table 11. In the table, the probability quoted is the probability per decay that the corresponding emission species will be produced.

Table 11: Decay Products of the Radioactive X-Ray Sources Used for IPC Calibration

Thermal Cycling Equipment: The IPC response to temperature variations was tested by placing the IPC on a VWR Scientific Series 400 HPS hot plate. An insulating cover, the "bake-o-matic" was made of two cardboard boxes of different sizes with insulation filling the gap between them. To measure the temperature of the IPC body an Omega model HH21 thermocouple was used.

Next Page

Previous Page

Top of Page

Table Of Contents