COPS Instrument Modes T. Semon K. Altwegg University of Bern Physikalisches Institut Sidlerstrasse 5 CH-3012 Bern Switzerland {| TABLE !Document Reference: !!RO-ROS-MAN-1019! |- |Issue: 1 ||Rev.: 7 |- |Date 04. 1. 2011 ||Pages: 14 |} {{{Document Change Record}}} {| TABLE !Issue !!Rev. !!Pages changed, added, removed !!Date !!Reasons for Changes !! Approval ! |Issue |Rev. |Pages changed, added, removed |Date |Reasons for Changes |Approval | |1 |- |All |16-11-2001 |Initial Issue | | |1 |1 |All |26-11-2001 |Updates proposed by Kathrin Altwegg | | |1 |2 |Page 7,9 |06-12-2001 |Add flux formula Add DPU Action Mode | | |1 |3 |All |19-12-2001 |Consolidation by K. Altwegg | | |1 |4 |All |21-01-2002 |Optimization task and sequence deleted RN and RM parameters added for the AMBiant task ALGorithm task and Data acquisition paragraph deleted New mode definition | | |1 |6B |7, 12-13 |27-09-2007 |Update to Software V6.B | | |1 |7 |All |5-01-2011 |Clean-up of document Addition of calibration | | |} Table of Contents Document Change Record 2{{ }}List of Abbreviations 3{{ }}1{{ }}Scope 4{{ }}1.1{{ }}Reference documents 4{{ }}1.2{{ }}Introduction 4{{ }}2{{ }}COPS Modes and measurement sequences 5{{ }}3{{ }}Explanations of the COPS Parameters 5{{ }}3.1{{ }}Channel 5{{ }}3.2{{ }}Task 5{{ }}4{{ }}Measurements 6{{ }}4.1{{ }}Offset 6{{ }}4.2{{ }}Timing 7{{ }}5{{ }}Mode numbering 7{{ }}6{{ }}Tables necessary to run COPS autonomously 8{{ }}6.1{{ }}Calibration overview (S. Graf, 2003) 9{{ }}6.1.1 COPS-FS Nude Gauge calibration 9 6.1.2 COPS RAM Gauge calibration 12 6.1.3 Conclusions 13 7{{ }}Table of General settings 14{{ }}8{{ }}A word of Caution: 17{{ }} {{{List of Abbreviations}}} COPS Comet Pressure Sensor DPU Digital Processing Unit FM Flight Model (which is the one in the lab) FS Flight spare model (which is the one flying) HK Housekeeping ROSINA Rosetta Orbiter Spectrometer for Ion and Neutral Analysis S/C Spacecraft TBD To Be Defined TBC To Be Confirmed {{{ Scope}}} The Comet Pressure Sensor will measure the ambient total density as well as the comet ram pressure. These two quantities can be used to derive the speed and the Mach number of the cometary gas. COPS will also serve as a pressure monitor for safety purposes. It will distribute the total pressure to all Rosetta instruments via service 19. This document contains the COPS instrument modes and measurement sequences. {{Reference documents}} |Nbre |Institution |Document Title |Reference |Issue | |[1] |UoB |EID-B: ROSETTA-Rosina Experiment Interface Document |RO-EST-RS3013/EID B |Issue 1, Rev. 0 15-01-1999 | |[1] |UoB |Rosina Users Manual |RO-ROS-MAN-1007 prepared by Kathrin Altwegg |Draft 2, Rev. 0 19-09-2000 | {{Introduction}} The Comet Pressure Sensor (COPS) consists of two gauges. The first gauge called "nude gauge" measures the total pressure (more exactly the density) of the comet gas. The second gauge called the "ram gauge" measures the ram pressure (equivalent to the comet gas flux). The nude gauge uses filaments to emit electrons and to ionize the gas, the ram gauge uses microtip arrays. {{{ COPS Modes and measurement sequences}}} COPS Instrument Parameters Settings |Channel |NUDe gauge | | | |RAM gauge | | | |BOTh | | |{{Task}} |NONe | | | |AMBient{ RN, RM } | | | |OFfSet | | |{{Emission}} |EMIssion{ Fil, Mic, IF, IM } | | {{{Explanations of the COPS Parameters}}} To measure the pressure, COPS can work with the both gauges (nude and ram gauges) or just one. {{Channel}} The NUDe gauge mode is used for monitoring purposes. In case there is not enough power available the RAM gauge mode (which uses less power) can also be used for monitoring, however the result is somewhat less precise. The mode BOTh is the science mode of COPS. From this mode only the gas dynamics can be derived. {{Task}} AMBient means that the instrument measures the cometary (asteroidal, spacecraft background) ambient pressure. The RN (nude gauge range) and RM (ram gauge range) parameters indicate the operating electrometer range. RN / RM : nude/ram gauge electrometer range 0 = Automatic range by the DPU 1 = Low 2 = Medium 3 = High OFfSet is the measurement of the offsets of one or both gauges. EMIssion means that the COPS set up the voltages to have the specified emission. The parameters that set the emission current and the active emitter(s) are: Fil (1bit): 0 for left filament or 1 for right filament active. Mic (8 bits): Microtip group status Bit 1: Mic 1 status (0 = disable, 1=enable) Bit 2: Mic 2 status (0 = disable, 1=enable) Bit 3: Mic 3 status (0 = disable, 1=enable) Bit 4: Mic 4 status (0 = disable, 1=enable) Bit 5: Mic 5 status (0 = disable, 1=enable) Bit 6: Mic 6 status (0 = disable, 1=enable) Bit 7: Mic 7 status (0 = disable, 1=enable) Bit 8: Mic 8 status (0 = disable, 1=enable) The current levels (parameters II and IM) set the filament and the microtip(s) emission. II (0-3): emission filament to 100uA low ion, 15uA low ion, 15uA med ion, 15?A high ion IM (0-3):: emission microtip(s) to 100uA, 15uA, 50uA, not used {{{Measurements}}} {{Offset}} When commanding a COPS measurement mode the first step is to determine the electrometer offsets. In order to do so, the electron emission has to be turned off. In the offset measurement mode, which can be selected / deselected when commanding any measurement/monitoring mode the instrument will switch through all three sensitivity levels of the electrometers and record the offset values. This takes appr. 5 min. due to the fact that the values are transmitted in the normal housekeeping data (1 value per minute). The subsequent measurements and monitoring modes are indefinite in time. No renewal is necessary. After every 24h after the end of the previous offset measurement the DPU will again command an offset measurement mode which takes appr. 25 min (5 min for the offset, 20 min to switch on the filaments/microtips again). In order not to have the complete instrument inactive for this time the offset measurements of the nude gauge and the ram gauge are timed 12h apart. When designing a measurement sequence for ROSINA this has to be taken into account. The new 24h interval starts once COPS is again in measurement mode, that is appr. 24h 25m after the start of the previous one. {{Timing}} COPS pressure measurements are read out by the DPU every two seconds. However, the internal integration time is appr. 10s due to the time constant of the electrometers. What is read out is therefore a running average over the last 10 s. The DPU itself builds a running average over the last 5 measurements. This value is transmitted in the normal monitoring modes once every minute. The time stamp of this value has therefore to be corrected by -5s. COPS also has a scientific mode which can be commanded independently of the normal measurement mode. In this mode all read mout housekeeping are transmitted in science blocks containing 150 data points (5 min) for each gauge. In this mode the correction of the time stamp is -1s. However, it has to be kept in mind that the time resolution is not really 2s but 10s as given by the electrometers. {{{Mode numbering}}} The numbering of the Mode used the following last digits (combination of channel and task): 0: General for COPS Instrument / DPU action modes 1: NUD, OFS 2: NUD, AMB{ RN, RM } 3: RAM, OFS 4: RAM, AMB{ RN, RM } 5: BOT, OFS 6: BOT, AMB{ RN, RM } The numbering should be arranged as follows: 0 to 49: Basic modes for switch on/off 49 to 99: Basic offset modes 100 to 299: Basic emission modes 300 to 499: Standard survey modes 500 to 999: Custom modes {{{Tables necessary to run COPS autonomously}}} To calculated the pressure, the DPU use the following formula: For the nude gauge: For the ram gauge: The Ion offset value is measured in background mode. S is the calibration factor, it is about 30 for the nude gauge and 5 for the ram gauge. This factor depends of the temperature and the ambient gas. Flux formula for the Ram gauge: phi_out = gas flux [1/m2*s] kB = Boltzmann-constant = 1.38e-23 [J/K] T_RG = ram gauge temp. [K] mass = 18 amu = 2.9889e-26 [ Kg] (H2o is the default mass) p_RG = ram pressure [Pa] = 100*[p(mbar)RG] The pressure values given directly in the COPS housekeeping are pressures for N2 at 20 DegC. In order to derive the density this pressure value has therefore to be converted to density as follows: n (m-3) = p /(kT) with p in Pa; T=293K, k=1.380 * 10-23 J/K e.g. if p=1x10-10 mbar n=2.4x1012 m-3 = 2.4x106 cm3 {{Calibration overview (S. Graf, 2003)}} All measurements were performed with COPS mounted at CASYMIR (CAlibration SYstem for the Mass spectrometer Instrument Rosina) Reference gauge : Granville-Phillips Stabil-Ion (Series 370) ionization gauge Argon was used as the calibration gas for all measurements over a pressure range from ~5*10-10 to ~1*10-6 mbar All pressure values are normalized for Nitrogen One single data point represents the average over 20 house keeping values taken within 40 s Pressure calibration with and without offset: -As the calibration was done over several orders of magnitude the least squares fit was performed using relative errors instead of absolute differences => rel. errors will be similar in the low and high pressure range {COPS-FS Nude Gauge calibration} The two filaments of the Nude Gauge were calibrated in 3 different modes: 1.High emission with 100 uAand low ion current (< 100 pA) 2.Low emission with 5 or 15 uAand low ion current 3.Same as above but with medium ion current (> 100pAup to 10000 pA) {COPS RAM Gauge calibration} All 8 microtipgroups were used in the following modes: 1. High emission with 100 uA and low ion current (< 100 pA) 2. Low emission with 5 or 15 uAand low ion current Additionally some measurements at 15 uAemission were performed with a single group. Although fits a) and b) are very similar, collecting all data points into one fit introduces large errors for low pressure values. -Proportional fits are only usable for high pressure values, above ~10-8 mbar. Errors for lower calibration points are large,> 100%! -The RAM Gauge sensitivity is roughly 4 times lower compared to the Nude Gauge. {Conclusions} -Very good agreement between the Stabil-Ion reference gauge and both COPS models, rmserrors for the linear fits are below 5% -The FS NG sensitivity is between 19 to 23 mbar-1or about 2 A*bar-1at 100 uAemission -The FM sensitivity is lower compared to the FS,up to 16% for the NG and 20% for the RG -The RAM Gauge sensitivity is about 4 times lower compared to the Nude Gauge and the offsets in the linear fits are higher {{{Table of General settings }}} In this table are the parameter values in function of the mode. Table Legend: x : means that the value is defined by the last mode The COPS Instrument Modes are detailed in a separated document named COPS_MODE_DESC.ASC M322 and M326 are the normal monitoring modes with automatic scaling, the nude gauge only and both gauges respectively. {{{A word of Caution:}}} The microtips have to be switched on very carefully after a prolonged period of non-operation. For this a commissioning phase has to be foreseen, especially after hibernation. Such a commissioning was last performed in 2006 (PC4). The same procedures can be used again. Use ARN070A with the following parameters: |C2_Function 10, condition microtip groups 1-3, at the end of this sequence COPS is in stby |ZRNC2003 |PRNGG206 = 10 PRNGG207 = 1 PRNGG208 = 3 PRNGG209 = 18 PRNGG20A = 60 | |C2_Function 10, condition microtip groups 4-6, at the end of this sequence COPS is in stby |ZRNC2003 |PRNGG206 = 10 PRNGG207 = 4 PRNGG208 = 6 PRNGG209 = 18 PRNGG20A = 60 | |C2_Function 10, condition microtip groups 7,8, at the end of this sequence COPS is in stby |ZRNC2003 |PRNGG206 = 10 PRNGG207 = 7 PRNGG208 = 8 PRNGG209 = 18 PRNGG20A = 60 | Each command needs appr. 8h.