Operating Instructions for the Optical Link Current Source ----------------------------------- Rev. 24-MAY-1993 Initial Testing after receiving the current source ---------------------------------------------------- 1. The Digital Box should be tested first by itself. The optical link should NOT be connected between the Digital Box and the Analog Box and the Digital Box should NOT be supplying +- 15 Volt power to the Analog Box. 2. Set the Digital Box controls as follows: Power: Off Sweep Rate: 315 Sweep Target Code Selection: Fixed (Down) Variable Sweep Target Code: 8ABC Sweep Select: Automatic (Center) Fixed Sweep Target Code Toggle Switches: All Down except "Zero" and "POS" should be Up Current Load: External (up) i.e. the cryostat 3. Plug the Digital Box into 240 Volt AC power. I have set the rear panel line voltage selector for 240 Volt and I have been running the box on 230 Volt 60 Hz. I have included a power cord with the U.S. plug cut off. The equipment end of the cord is the international standard connector so I expect that you have have a proper cord with a British end on it. If not the color code is: Color U.S. Name Function -------------- --------------- ---------------- Green/Yellow Safety Ground Safety Ground Brown Hot (phase) power Blue Neutral power 4. Turn the Power switch ON and the following should happen. The +5 Volt LED will light immediately. After some seconds (0 to 15) the DAC Stable LED will light and the DAC Code Hexadecimal display will read 8000. 8000 is the DAC Code for zero output (0001 is Negative Full Scale, and FFFF is the Positive Full Scale DAC Code). 5. Flip the "Zero" Fixed Target Code toggle switch Down and flip Up the Full Scale toggle switch (the 1.0 switch). Press the Sweep push button. As soon as you press the Sweep push button the DAC Stable LED will go out and the DAC Code Hex Display will start to sweep up. After some seconds the DAC Stable LED will light and the Hex Display will read FFFF (i.e. Positive Full Scale). 6. Flip the "POS - NEG" toggle switch Down and press the Sweep push button. This time the Digital Control Box will sweep down to DAC Code 0001 (i.e. Negative Full Scale). 7. Sweep back and forth between plus and minus Full Scale trying different Sweep Rates. The fastest that you can go is 15 usec per DAC Code (i.e. 015 on the lever wheel switch). At this setting it will take only a second or two to sweep from full scale in one polarity to full scale in the other polarity. At 999 usec per DAC Code it will take 65 seconds to make this sweep. 8. Try sweeping to different Fixed Target Codes. The corresponding Hexadecimal DAC Codes to look for in the Hex Display are listed in the main section of the instructions. 9. Try Sweeping to a Variable Sweep Target Code. Flip the Variable/Fixed Sweep Target Code Selector toggle switch Up to select Variable Target Codes. Set the desired Target Code in the Variable Sweep Target Code Hexadecimal lever wheel switches and push the sweep button. After an appropriate delay the DAC Stable LED will come back on and the Hex Display will read the same as the Target Code that you have dialed on the Variable Sweep Target Code level wheel switches. 10. The Sweep Rate selection will work the same when using the Variable Target Codes as it did when using the Fixed Target Codes. 11. Try the Force Up and the Force Down positions of the Sweep Selection toggle switch. When in a Force position the DAC Stable LED will stay off and the Hex DAC Code Display will roll over (e.g. FFFF --> 0000 when sweeping up). When in a Force position the Sweep Rate switch will work the same as in Fixed or Variable Target Code sweeping. 12. On the rear panel of the Digital Box check the Isolated 15 Volt Power Supply output with a Volt Meter. These supplies should be within a hundred mV of 15 Volts. Note: The Positive lead of the Negative 15 Volt supply is common with the Negative lead of the the Positive 15 Volt supply. This common is NOT connected to the case or chassis of the Digital Box at any point. The word "Isolated" refers to these supplies being well isolated from the AC line power not to the negative supply being isolated from the positive supply. The center post on the output terminal strip (Labeled "CH") is connected to the CHassis of the 15 Volt power supply and NOT to the case or chassis of the Digital Box as a whole. The chassis of the 15 Volt power supply IS isolated from the case and chassis of the Digital Box. The chassis of the 15 Volt power supply is also isolated from its common output terminal. See the main section of the instructions for more details about this power supply. 13. Remove the Dust Caps from the optical link connections on the Digital Box. SAVE these Dust Caps. The three optical transmitters labeled: Data, Clock, and Load should show a visible Red light. The optical transmitter labeled Int/Ext should show a visible Red light when the front panel Current Load toggle switch is in the INT (Down) position. 14. If everything is OK so far then the Digital Box must be mostly working so it is now rational to test the Analog Box which depends on the Digital Box for its proper operation. 15. Turn OFF the Digital Box. 16. Preset the controls on the Analog Box. Power: OFF Current Range: 100 ma Current Zero : This control should be very close to its proper position. Do not move it at this time. A reading of 602 is about the proper position of this Current Zero control. 17. Connect the DC power cable to carry the Isolated 15 Volt power from the Digital Box to supply the Analog Box. At each end of the DC power cable there are two wires connected together with clear insulation. These are the shields of each section of the DC power cable and are connected to the terminals labeled "CH" at each end. To connect to the terminal strips loosen the screw so that it is not compressing the contact leaf at all, then with a very small screw driver push the contact leaf back out of the way (i.e. push it toward the screw) to make room for the wire on the DC power cable. If the leaf is fully back out of the way then the wires on the DC power cable fit very nicely into these terminal strips. I have included a spare terminal strip in case a screw is lost from a terminal strip on one of the boxes. I have tightened the screws on the terminal strips on the boxes so that they to not fall out during shipping. 18. Connect the Optical Link. Save the dust caps and the sacks that protect the ends of the optical cables. 19. Connect the Current Output from the Analog box to a digital current meter that can read 100 ma. I have included the Trompeter to banana plug cable that I used to connect to a current meter. 19. On the Digital Box Select Internal Load. Turn on the Digital Box and the Analog Box. Sweep the Digital Box to Zero. Verify that the current meter reads zero. 20. Switch to External Current Load. This connects the Analog Box to the current meter. The current meter should still read very near zero. Adjust the Analog Box front panel Current Zero knob for a zero reading on the current meter. It may be best to wait a few minutes for things to "warm up" before making this adjustment. The proper setting on the Zero Current knob should be close to 602. 21. Use the controls on the Digital Box to sweep the Analog Box to positive full scale. The current meter should read very close to + 100 ma. Sweep the Digital Box to negative full scale. Now the current meter should read - 100 ma. 22. Try some other Sweep Target Codes (e.g. Fixed Target Codes: 0.5, 0.1) and verify that the current meter reads as expected. Try some other settings of the Current Range switch on the Analog Box and verify that the current meter reads as expected. General Instructions ---------------------- Digital Box ------------- 1. Sweep Rate. The Sweep Rate lever wheel switch sets the number of microseconds that the DAC stays at a given code before incrementing or decrementing to the next code. Use only settings between 015 and 999. Settings under 015 will cause the DAC to begin loading the next code before it has stabilized on the current code. For most normal work it is probable only necessary to move the most significant position of the Sweep Rate switch. The following table gives the approximate time required to sweep from zero to full scale for a number of settings of the Sweep Rate switch. Sweep Sweep Rate Time to Sweep from Rate Time to Sweep from us/code Zero to Full Scale us/code Zero to Full Scale ------- -------------------- ------- -------------------- 015 0.49 seconds 515 16.87 seconds 115 3.77 seconds 615 20.15 seconds 215 7.04 seconds 715 23.43 seconds 315 10.32 seconds 815 26.70 seconds 415 13.60 seconds 915 29.98 seconds 2. Variable Sweep Target Codes. You can use the Variable Sweep Target Codes to pick any output current that you want. Refer to the i-Source DAC Code table to understand the basic mapping of the Digital Box DAC Codes. As an example assume that you want an output current of 79.44 ma. You could set the Analog box on the 100 ma range and then calculate the required setting of the Variable Sweep Target Code switch. 79.44 ma desired current X = ------------------------- x 32,767 Full Scale DAC Code 100 ma full scale range For a positive current add 32,768 to the above number, convert it to hexadecimal and set it in the Variable Sweep Target Code switch. For a negative current subtract the above "X number" from 32,768 convert it to hexadecimal and set it in the Variable Sweep Target Code switch. 79.44 ma desired current ------------------------- x 32,767 Full Scale DAC Code = 26,030 100 ma full scale range 26,030 + 32,768 = 58,798 = $E5AE DAC Code for +79.44 ma 32,768 - 26,030 = 6,738 = $1A52 DAC Code for -79.44 ma 3. Isolated Power Supply. The +- 15 Volt Isolated Power supply in the Digital Box can provide between 800 ma and 1000 ma of current on each of its outputs (i.e. the fold back current protection will start somewhere between 800 and 1000 ma). The outputs from this supply pass through internal 2 Amp fuses before reaching the rear panel terminal strip. AC line power for this Isolated Power Supply passes through an isolation transformer before reaching the supply. The frame, core iron, and shield of this isolation transformer are connected to the overall case and chassis of the Digital Box and thus to the Safety Ground on the power cord. The chassis and the input transformer of the Isolated Power Supply are isolated from the overall case and chassis of the Digital Box. The frame, core iron, and shield of the input transformer on the Isolated Power Supply are connected only to the isolated chassis of this power supply. The isolated chassis of this power supply is only connected to the "CH" terminal in the center of the rear panel Isolated Power Supply terminal strip. Connecting the shields on the DC power cord that runs between the Analog Box and the Digital Box to the "CH" terminals at each end will connect the input transformer shield and the chassis of the Isolated Power Supply to the same ground potential as the cryostat. All of the digital electronics in the Digital Box will remain "floating" from the cryostat ground. I expect that there will still be too much capacitive AC coupling of noise on this Isolated 15 Volt Power Supply for actual use with a SQUID but the hope is that this 15 Volt power will be quiet enough to use when setting things up. The 15 Volt Isolated Power Supply in the Digital Box may also be used to operate some other equipment when it is not being used to power the Analog Box. 4. Sync Output (rear panel). The rear panel of the Digital Box has a BNC connector labeled Sync Output. This is an active low TTL signal with an internal 100 ohm isolation resistor. This signal shows when the DAC Code Counter is at a particular value. The "sync value" of interest can be set on an internal 16 position DIP switch. Right now this is set for $7FE0 i.e. about 30 counts negative of zero. The Sync Output can be used to trigger a scope or some other piece of equipment as the Digital Box sweeps past a particular DAC Code. Analog Box ------------ 1. Current Range Switch. The Analog Box Current Range switch sets the full scale current range. The current scaling resistors on this switch directly set the full scale current range. These are all precision metal film resistors (0.02% accuracy or better and 10 ppm per degree C or better) except for the resistors installed in the 2 ma, 1 ma, and 500 ua settings. The good resistors for these 3 settings had not arrived by the time this unit was shipped. Right now I have unknown accuracy resistors of 50 ppm per deg C installed in these 3 locations. The Current Range switch also includes a Voltage Output position at the most clockwise location. You should only switch to the Voltage Output position when the output has been ramped to zero. You should not select the Internal Current Load when the Voltage Output mode has been selected. When operating in the Voltage Output mode the external load should be 30 ohms or more to prevent exceeding the maximum current output from the Analog Box. When in the Voltage Output mode the Analog Box will look like a voltage source with in internal 20 ohm resistance. The full scale output in the Voltage mode is 5.000 Volts. 2. Rear Panel Battery Connections. The Analog Box rear panel battery connections are for the positive and negative 12 Volt batteries. Inside the Analog Box the positive lead of the negative battery is connected to the negative lead of the positive battery. The input from each battery passes through a fuse and then after the fuse there is a reverse polarity protection diode across each battery. If one of the external batteries is connected backwards then the fuse inside the Analog Box should be forced to blow by the reverse polarity protection diode. The hope is that this will protect all of the electronics in the current source which would otherwise be damaged by reverse polarity power. The front panel LED's will light only when power is being properly supplied to the Analog Box. The center terminal on the rear panel battery connection terminal strip is labeled "CH" for chassis. This connects only to the metal chassis of the Analog Box (it has NO connection to the current source electronics in the Analog Box). The "CH" terminal is connected to the shield on the Trompeter cable and thus to the cryostat. The "CH" terminal can be connected to the shield on the power cable between the Analog Box and the box holding the 12 Volt batteries. At the battery end of this power cable its shield could be connected to the battery box thus holding the battery box at the same ground as the cryostat. The quiescent current drain on the positive battery is about 180 ma and on the negative battery it is about 50 ma. About 100 ma of the load on the positive battery is due to the relays that switch between the Internal and the External Current Loads. These relays draw the same current in either load position (i.e. there are 4 relays and the coils on one set of 2 or else the other set of 2 are always energized). 3. Percent of Full Scale Output Current Meter. This absolute value meter on the Analog Box reads the actual percent of output current flowing through the load. This is independent of the setting of the Current Range switch on the Analog Box. If the current load circuit in the cryostat were to open then this meter would always read zero no matter where you had swept the Digital Box. Test of the i-Source that were made before shipping ------------------------------------------------------- 1. Output stability and freedom from oscillations and noise. Using a scope and a storage scope I checked the output for noise and oscillations under a number of conditions. These included: I checked the output when there was a large capacitive load on the current output to see if the Analog Box could be forced to oscillate. I used 0.1 ufd capacitors (and larger) to simulate the filters on the cryostat. I check the output on a storage scope as the DAC swept through its most significant carry to verify the trim on its MSB and its dynamic performance. I checked the output on a storage scope as the Current Load was switched from Internal to External and visa-versa. 2. I checked the leakage current from the electronics in the Analog Box to the case of the Analog Box (i.e. to the shield on the Trompeter cables, i.e. from the current source electronics to the cryostat). This is less than 10 to the minus 10 Amps with 10 Volts between them. 3. I checked the current output for accuracy using the Fluke 8842A multimeter. This 5 1/2 digit meter has a most sensitive current range of 200 ma, it resolves 1 ua, it has a 0.1 ohm input shunt resistor (i.e. it is looking at 100 nano Volts), the accuracy when 2 years out of calibration is 0.08% +- 40 counts. The +- 40 counts is, I assume, all just offset which I "took out" with the meters offset button. Full Scale Current Meter Reading at the Fixed Sweep Target Current ----------------------------------------------------- Range + 1.0 - 1.0 + 0.5 - 0.5 ------------ ----------- ----------- ----------- ----------- 100 ma +99.997 ma -99.998 ma +49.998 ma -50.002 ma 50 ma +50.005 ma -50.004 ma +25.003 ma -25.002 ma 20 ma +20.001 ma -19.998 ma +10.001 ma -9.998 ma 10 ma +10.001 ma -9.997 ma +5.001 ma -4.999 ma 5 ma +5.000 ma -4.997 ma +2.500 ma -2.498 ma 2 ma +2.002 ma -2.003 ma _ _ 1 ma +1.001 ma -1.000 ma _ _ 500 ua +0.501 ma -0.499 ma _ Not _ 200 ua +0.200 ma -0.199 ma _ Checked _ 100 ua +0.100 ma -0.100 ma _ _ Next I checked all of the Fixed Sweep Targets on the 100 ma full scale Current Range. Current Meter Current Meter Fixed Sweep Reading Reading Target Code Positive Target Negative Target ------------- ----------------- ----------------- 1.00 + 99.997 ma - 99.992 ma 0.90 + 89.998 ma - 89.993 ma 0.75 + 74.996 ma - 74.992 ma 0.50 + 49.998 ma - 49.997 ma 0.20 + 19.999 ma - 19.996 ma 0.10 + 10.001 ma - 9.997 ma E-2 + 1.002 ma - 0.998 ma E-3 + 0.102 ma - 0.098 ma E-4 + 0.011 ma - 0.007 ma