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Plexon Stimulator 2.0 Manual Download Page 27

 

 

Neurotechnology Research Systems

 

© Plexon Inc

 

 

  - 27 -

 

5.9

 

Impedance measurement 

Impedance measurement is a typical means of characterizing electrodes.  Impedance measurement 
is typically accomplished by applying a very low amplitude sinusoidal current to the electrode and 
monitoring  the  resulting  voltage  developed  across  the  electrode.    The  stimulator  has  a  special 
impedance measurement (Z-test mode) that automatically generates a ±100 nA 1 kHz sinusoid for 
impedance testing. 

Locate the “Function” control towards the bottom of the GUI: 

 

Press the “Z-test” button to put the stimulator in impedance test mode: 

 

Notice that the Vmon scaling control changes and the default setting is now 4000 

/mV

pp

. 

The  controls  for  all  channels  become  grayed  out  and  a  pre-defined  arbitrary  waveform  pattern 
called “Z-test” that codes for a ±100 nA 1 kHz sinusoidal current is automatically loaded for every 
channel: 

 

Click the start button to begin generating the sinusoidal current on channel 1: 

 

Summary of Contents for Stimulator 2.0

Page 1: ...0 April 2011 Plexon Inc 6500 Greenville Ave Suite 700 Dallas Texas 75206 United States of America Tel 214 369 4957 Fax 214 369 1775 E mail info plexon com www plexon com Stimulator 2 0 April 2011 STI...

Page 2: ...lexon Inc and it is proprietary and restricted solely to assist Plexon Inc customers Neither this document nor the contents may be disclosed copied revealed or used in whole or in part for any other p...

Page 3: ...angular pulses 18 5 5 Verifying the output on an oscilloscope 19 5 6 Compliance voltage and stimulation failure 22 5 7 Automatic electrode discharge 24 5 8 Arbitrary Waveforms Complex Rectangular Puls...

Page 4: ...Vmon scaling Z test mode 41 6 6 3 Z conversion 42 6 7 Function Stimulate Function Z test 42 6 7 1 Stimulate Mode 42 6 7 2 Impedance Test Mode 42 6 8 Trigger Mode 43 6 8 1 Software Trigger Mode 43 6 8...

Page 5: ...Waveform Pattern Files 54 9 Stimulator Limitations 55 9 1 Maximum Compliance Voltage Varies with Stimulation Amplitude 55 9 2 Power on off Transients 55 9 3 Current Monitor with an Open Circuit 56 9 4...

Page 6: ...may be used in an edge triggered or level triggered gated mode to initiate stimulation with microsecond latency Each channel also has a dedicated digital output to signal to other devices the precise...

Page 7: ...n 14 20 A 10 A 7 Stimulation Cable Plexon 14 03 A 03 8 Test Board model electrodes Plexon 14 04 A 03 A International customers The stimulator power supply has an International Electrotechnical Commiss...

Page 8: ...tion Read the entire Driver Installation section before proceeding with any of the steps 4 1 1 Browse to the folder Stimulator Driver on the USB flash drive and run the program CDM20802_Setup exe On s...

Page 9: ...wse to the Stimulator Software folder on the USB flash drive 4 2 2 Double click the file Stim 2_Setup exe to begin the installation process On some computers you will get a warning 4 2 3 Click Yes or...

Page 10: ...Plexon Inc The default install location for Windows XP is C Program Files Plexon Inc Click Next to continue 4 2 5 You will be asked to confirm that you would like to start the installation Click Next...

Page 11: ...Neurotechnology Research Systems Plexon Inc 11 4 2 7 Once the progress bar starts moving the installation completes quickly Click Close to complete the software setup...

Page 12: ...the power switch on the power supply is in the off position 4 3 2 Connect the AC power cord between the AC outlet and the power supply 4 3 3 Connect the DC power cord between the power supply and the...

Page 13: ...een the stimulator and the test load board Be sure to line up the white orientation dots on both connectors 4 3 7 Connect BNC cables between the monitor channel outputs and an oscilloscope Monitoring...

Page 14: ...and corner of the computer screen In Windows 7 the balloon changes from Installing device driver software to Your device is ready to use In Windows XP the balloon cycles through several different disp...

Page 15: ...fixed rate More complicated rectangular waveforms and non rectangular arbitrary waveforms may be defined in and loaded from a simple text file Once defined the stimulation pattern is downloaded into...

Page 16: ...ate Rectangular Pulses First phase amplitude and width Interphase delay Second phase amplitude and width Number of pulses Rate Trigger Mode Load Start Monitor Arbitrary Waveform Load File Number of pu...

Page 17: ...efault configuration at any time by selecting Open from the File menu and then selecting the configuration file Factory_Default stm By default this file is installed in the directory C PlexonData Stim...

Page 18: ...nter phase delay The first phase is 100 A for 50 s the inter phase is 0 A for 25 s and the second phase is 100 A for 50 s To make it easier to see on the oscilloscope we want to generate a continuousl...

Page 19: ...rrent monitor is 2 5 mV A and by default the scale factor for the voltage monitor is 0 25 V V That means that if there is a 100 A current flowing into the electrode from the stimulator the current mon...

Page 20: ...s law with respect to the access resistance of the electrode The subsequent rise in electrode voltage during the first phase of the pulse is due to charging of the electrode capacitance By definition...

Page 21: ...ltage immediately drops by the same amount that it jumped at the beginning of the pulse VACCESS The current during the interphase period is zero With no current flowing into the electrode there is no...

Page 22: ...col will depend on the amplitude of the current pulse the duration of the pulse the stimulator compliance limit and the properties of the electrode To see this effect first stop the ongoing stimulatio...

Page 23: ...he monitor channel At this point the compliance limit has been reached and the output current as seen on the current monitor drops to zero The voltage however stays at its maximum value just to mainta...

Page 24: ...returns to zero after the end of the pulse Ordinarily if the pulse delivery was not balanced and charge was left on the electrode then the voltage of the electrode would change after each pulse The o...

Page 25: ...of rectangular pulses than can be defined using the front panel GUI controls The format of the arbitrary waveform text file is defined in section 6 5 To load an arbitrary waveform for channel 1 make...

Page 26: ...search Systems Stimulator 2 0 26 Change the No of repetitions to be 2 and the Rate to 1000 Hz Then Load and Start the channel The output of the stimulator is Rate 1000 Hz 1 ms One waveform Repeated tw...

Page 27: ...Z test mode that automatically generates a 100 nA 1 kHz sinusoid for impedance testing Locate the Function control towards the bottom of the GUI Press the Z test button to put the stimulator in imped...

Page 28: ...peak amplitude of 7 60 mV Try changing the Vmon scaling from 4000 mVpp to 400 mVpp Now the output of the voltage monitor is a sinusoid with a peak to peak amplitude of 76 8 mV Continue to change the...

Page 29: ...litude signal on the voltage monitor is 856 mVpp and the Vmon scaling is 40 mVpp so the impedance of the electrode is To obtain the most accurate impedance reading you should adjust the scale factor a...

Page 30: ...ity of the electrode tissue interface over time This section shows some measurements obtained from a blunt cut 25 m diameter platinum iridium micro wire electrode in saline All of the measurements are...

Page 31: ...increase in electrode voltage from 1 64 V to 2 64 V over the course of the 50 s pulse implies a capacitance of It is tempting to try and relate the impedance of the electrode at 1 kHz to the stimulat...

Page 32: ...ger modes Rising and Level In the rising trigger mode stimulation begins when the digital input for the channel transitions from low 0V to high 5V In the level trigger mode stimulation also begins whe...

Page 33: ...letion Compare that with the output in Level trigger mode To switch to level trigger mode you must first change channel 1 to edit mode Then switch to level trigger mode Finally load channel 1 again Th...

Page 34: ...e user interface Pressing the Stop or Edit control for a particular channel causes the stimulation in progress on that channel to stop Pressing the Stop All Edit All or Abort controls or closing the u...

Page 35: ...the channel is in edit mode Press the Edit button to put the channel in edit mode Pressing the edit button will cause any stimulation pattern that is in progress on the channel to stop 6 1 2 Load Onc...

Page 36: ...orm output the remainder of that pulse or arbitrary waveform will play to completion This helps preserve charge balance in the stimulation output Any remaining pulses in the pattern will not be played...

Page 37: ...d second phases The interphase delay may range from 5 s to 65535 s in steps of 1 s The current output is zero during the interphase delay 6 3 4 Second Phase Amplitude The second phase amplitude may ra...

Page 38: ...r arbitrary waveform is repeated expressed in Hertz or the time between the start of one pulse or arbitrary waveform and the start of the next pulse or arbitrary waveform expressed in milliseconds Use...

Page 39: ...o arbitrary waveform pattern file formats are supported One file format uses a fixed sampling rate and the other file format uses a variable sampling rate 6 5 1 Fixed Sampling Rate In the fixed sampli...

Page 40: ...le code for additional amplitude duration pairs When the stimulation pattern is played back each current amplitude is played for the specific duration associated with that amplitude The variable sampl...

Page 41: ...g with extremely low impedance electrodes Divide the voltage observed on the monitor output by the scale factor to determine the voltage at the electrode Note that if the Vmon scaling is set higher th...

Page 42: ...nitor scale factor is handled automatically for you 6 7 Function Stimulate Function Z test 6 7 1 Stimulate Mode Select stimulate mode for rectangular pulse or arbitrary waveform stimulation 6 7 2 Impe...

Page 43: ...ated 6 8 2 Rising Edge Trigger Mode In the Rising trigger mode stimulation begins when the digital input for the channel transitions from low 0V to high 5V The latency from digital input to stimulatio...

Page 44: ...t during the stimulation pattern are ignored e g the pulse marked 3 6 9 Edit Load All When the Edit Load control is in Individual mode the mode of each channel can be configured using the individual E...

Page 45: ...sing the Start All function First define and load the appropriate stimulation pattern for the channels you wish to stimulate and then initiate the multichannel stimulation pattern by pressing the Star...

Page 46: ...eturn to the edit mode If the stimulator is in impedance test mode it will return to stimulate mode Consider a complete stimulation pattern that is composed of four pulses Pressing stop stop all edit...

Page 47: ...e parameters are then automatically re loaded the next time you open the user interface Note that if any channels have been configured to use an arbitrary waveform pattern neither the fact that the ch...

Page 48: ...ntentional electrode charging all electrodes are automatically discharged in between pulses and any time the channel is not stimulating Advanced users ONLY may disable the automatic discharge of the e...

Page 49: ...al There is also a 17th digital output that goes high when ANY channel is playing back a stimulation waveform Digital output 17 with digital output mode set to low during inter pulse interval Digital...

Page 50: ...s are TTL compatible 7 3 USB 2 0 The stimulator has a mini type B USB 2 0 receptacle for communications with the host computer The USB receptacle on the stimulator is connected to digital IO ground Th...

Page 51: ...goes high when any channel is stimulating See section 6 15 Options Digital Output Mode for additional details 1 DO 1 3 DO 3 5 DO 5 7 DO 7 9 DO 9 11 DO 11 13 DO 13 15 DO 15 17 DO 17 19 Dig IO GND 2 DO...

Page 52: ...the outer contact of the current monitor BNC connector is connected to analog IO ground The outer contact of the BNC connectors on many oscilloscopes is connected to the AC wall outlet ground Therefo...

Page 53: ...to the impedance of the electrode See sections 5 9 Impedance measurement and 6 6 Vmon scaling and Z conversion for additional details Note that the outer contact of the voltage monitor BNC connector...

Page 54: ...section 5 8 for an example of such a waveform created using the 3_pulse_burst_variable pat arbitrary waveform pattern file When using the GUI controls to define rectangular pulses the minimum interph...

Page 55: ...resistor is used to measure the actual output current but reduces the voltage available to deliver to the electrode 9 2 Power on off Transients To avoid transients at the stimulator outputs caused by...

Page 56: ...ient measured at the stimulator output is shown below For this reason disconnect the stimulator from the electrodes before turning the power off 9 3 Current Monitor with an Open Circuit Ideally when n...

Page 57: ...n the cabling to the electrode the impedance test procedure will yield a finite but large impedance result With no cable connected to the stimulator this open circuit impedance will vary from channel...

Page 58: ...rent 1 mA Stimulation mode Resolution 16 bits Output current resolution 30 nA Stimulation mode Compliance voltage 10 V 700 A see section 9 1 Temporal resolution 1 s Output rise time 1 25 s 100 A 10 k...

Page 59: ...Neurotechnology Research Systems Plexon Inc 59...

Page 60: ...Plexon Inc 6500 Greenville Ave Suite 700 Dallas Texas 75206 United States of America Tel 214 369 4957 Fax 214 369 1775 E mail info plexon com www plexon com Stimulator 2 0 April 2011...

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