EXPERIMENTAL CHEMISTRY II
EXPERIMENTAL CHEMISTRY II CH 461
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This 5 page Class Notes was uploaded by Dariana Wolff on Monday October 19, 2015. The Class Notes belongs to CH 461 at Oregon State University taught by Staff in Fall. Since its upload, it has received 44 views. For similar materials see /class/224556/ch-461-oregon-state-university in Chemistry at Oregon State University.
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Date Created: 10/19/15
CH 461 amp CH 46lH SWITCH s t NC Off quot I v RELAV I 5 l 7 iLH rcnt Sourtr to TEK Power Supply Module 5V N0 4 THO 5 I Vl l TimeCount Switch shown in Time position ONOFF for constant current generator Time Position SWITCH point S connected to Time and timer input connected to 60 Hz Count Position SWITCH point S connected to Off and timer input connected to Count socket Control Relay shown in NC lfVcontrol lt 25 V RELAY point S connected to NC normally closed lfVcontrol gt 25 V RELAY point S connected to NO normally open 085 r nul 39 I 7 Cm lpm39amr A l INITIALLY R53 is a 1000 ohm resistor dumm ce For experiment the 1000 ohm resistor dummy cell is removed amp replaced by the real cell OA 2 bottom of the LOGRATIO module input connected to variable voltage source which should be set to 085 V with DMM input INITIALLY connected to 5 V and then GND for experiment connected to PMT output Figure 2 Electronics setup Details about Programming the PTR CB3 at Station 7 for Wavelength Scans A Setting the Scan Rate The CB3 stepper motor controller sets the scan rate of the minichrom SDMC103 monochromator by controlling the step rate of a 09 degreeperstep stepper motor 800 stepsrev For the 03 monochromator there are 50 nmreV or 00625 nm step The desired scan rate can be calculated from equation 1 R ummin 375 VD eq 1 where V is the basic velocity and D is a diVider Values for common scan rates are shown in Table A Table A Parameters for scan rates using the CB 3 SR V D hmmin 535 divider 1 40 150 5 40 30 10 80 30 25 40 6 50 40 3 100 80 3 150 40 1 200 160 3 500 400 3 Slew 1000 1 B Programming the CB3 stepper motor controller for wavelength scans The CB3 is programmed by sending commands from a computer over an RS232 serial line You will operate the controller in command mode issuing commands from a PC which is running in the STEPPER MOTOR CONTROL or TERMINAL mode Boot up the computer select the TERMINAL icon from the CH 461 folder Now turn the power on to the CB 3 and strike any key on the keyboard Something similar to the following should appear on the screen V207 If not contact the instructor Once communication with the controller has been established you can begin to send commands The rst command that needs to be sent is E2 This command energizes the motor and prepares it to move this needs to be done every time you power up the CB 3 Commands are simply issued by typing them on the keyboard and hitting enter Examples of the commands you will use most often are listed in table B Table B Important commands for the CB 3 Stepper Motor Controller COMMAND DESCRIPTION Scan to the low wavelength mechanical stop with V1000 slew This position F10000 Find Home corresponds to the low limit wavelength listed in the monochromator specs e g 40 nm The stepper motor will step the desired of Step pOSitive decrease wavelength steps away from the current position Same as above only steps are in the Step negative increase wavelength negative direction Sets the stepping velocity see part I of this V Basic velocity handout All stepping speeds will be divided by this D Divider number Used in determining the stepping velocity see part I K Ramp Set the velocity ramp rate usually 0 Sets the origin We will usually set the O Set origin origin to the zero order of the monochromator Prints the current scan parameters on the X Examlne CRT screen Returns the current value of the position Z Read position counter Energizes the stepper motor This command E2 Energize needs to be entered before the stepper motor can be told to move De energizes the stepper motor coils This command should be executed whenever the motor is going to sit for long periods of time to prevent overheating E3 Deenergize Abort current command or scan Returns a uu ESC Escape key To use the CB 3 to choose a wavelength or do a calibrated wavelength scan the following information must be known First the step resolution of the monochromator is 00625 nm step This means that each step of the stepper motor will cause the monochromator to change its peak output wavelength by 00625 nm This also means that there are 16 stepsnm Thus to step 10 nm away from the current position requires exactly 160 steps of the stepper motor Also the direction of the stepper motor is opposite the change in wavelength eg Moving from zero to 100 nm is l600 steps Next the location of the zero order of the monochromator must be determined so that the position corresponding to 0 nm is known Fortunately this position should have already been determined and be written on a label on the monochromator e g 20 nm 330 steps The position of the zero order is referenced to a known point the low wavelength mechanical stop Thus to move the monochromator in the above example to its zero order type the following commands F10000 Find Home low wavelength 330 Move 330 steps in the 7 direction longer wavelength A white light image of the slit should now be visible at the focal point in the cell If this is not the case something is wrong This position is the reference point for all subsequent wavelength scans T 0 choose a speci c wavelength To calculate the number of steps from the zero order position use of steps l6 stepsnm X Min nm For example to move the monochromator to 500 nm you need to tell it to go 8000 steps 500 nm X 16 stepnm from the zero order position Table C The position of the stepper motor of the monochromator relative to the zero order for several wavelengths WAVELENGTH POSITION T 0 do a wavelength scan with Terminal For a wavelength scan go to zero order go to the starting wavelength set the scan parameters V and D for the desired scan rate and choose the number of steps to go to the end wavelength To do a wavelength scan with Monochromator Set the Initial Wavelength Enter a starting wavelength resolution 0125 nm in the Initial l box and then click Go to Initial to send the monochromator to the starting wavelength Do this at the start of each scan Prepare to Scan Enter an ending wavelength in the Final l box and select a Scan Rate and click Begin Scan Cancel Scan This button is available during a scan Press it to stop the current monochromator operation immediately Save Plot bottom of display window Click to write the output file and name it Other settings in Monochromator Channel to Plot bottom of display window We will use channel DevlaiO channel zero on the interface connector box39 other channels are available Voltage Range bottom of display window Selects for the Full Scale setting on the ADC board 200 mV39 l V39 5 V and 10 V are available The resolution of the signal changes with this setting Rnn Notes bottom of display window Place for comments that are included when the data are saved to the output file Zero Offset Enables operator to make small adjustment to the monochromator position scroll arrows and change the zero offset value when recalibrating zero order Set New Zero Offset After optimizing white light signal input the step number for the true zero order position 000 nm in the box called zero offset then close the program and reopen it The new zero order offset value should be displayed and it is stored in the OFFSETDAT file