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pico Technology PicoScope 3425, User Manual

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PicoScope 3425 PC Oscilloscope

10

Copyright © 2007 Pico Technology Limited. All rights reserved.

ps3425.en

2.6

What is a differential oscilloscope?

The PicoScope 3425 is a differential PC Oscilloscope.  A differential oscilloscope
measures the voltage difference between two points, regardless of the voltage of
either point with respect to ground.  This is unlike a conventional single-ended
oscilloscope, which requires one of the points to be at ground potential.

For example, suppose that you want to measure the output voltage of a transformer
with a grounded centre tap, as in the diagram below:

A single-ended oscilloscope can only measure a signal with reference to ground, so
you need to connect the scope's ground clip to the centre of the secondary.  You can
then measure either V

P

 or V

N

 with respect to ground, but not the total voltage across

the secondary.  The diagram below shows a single-ended scope connected between V

P

and ground:

With a differential oscilloscope, you can directly measure the secondary voltage by
connecting the positive probe to V

P

 and the negative to V

N

.  This is shown in the

diagram below.  A ground connection is not essential, although it is a good idea to use
a shielded cable grounded at one end in order to prevent electromagnetic noise
coupling into the cable.

Differential oscilloscopes have many other applications where the voltage to be
measured is not referenced to ground, or where it is not  desirable to connect the
scope ground to the ground of the device under test.

Summary of Contents for PicoScope 3425

Page 1: ...Copyright 2007 Pico Technology Limited All rights reserved PicoScope 3425 User s Manual ps3425 en 2 PC Oscilloscope ...

Page 2: ......

Page 3: ...oscilloscope 9 5 Specifications 10 6 What is a differential oscilloscope 11 7 Overflow indicators 11 8 AC DC coupling 11 9 Resolution enhance 12 3 Programmer s reference 12 1 Driver 12 2 Programming with the PicoScope 3000 Series 12 1 Voltage ranges 12 2 AC DC coupling 12 3 Triggering 13 4 Sampling modes 16 5 Oversampling 16 6 Scaling 16 7 Combining oscilloscopes 17 8 Functions 51 3 Programming ex...

Page 4: ...PicoScope 3425 PC Oscilloscope II Copyright 2007 Pico Technology Limited All rights reserved ps3425 en 59 Index ...

Page 5: ...d spectrum analyser Alternatively using the API functions you can develop your own programs to collect and analyse data from the oscilloscope 1 2 Minimum PC requirements For the PicoScope 3425 PC Oscilloscope to operate correctly you must connect it to a computer with the minimum requirements to run Windows or the following whichever is the higher specification Processor Pentium class processor or...

Page 6: ...illoscope is not designed for measurements on CAT II III or IV circuits The PicoScope 3425 PC Oscilloscope must not be directly connected to the mains line power Failure to heed this warning may lead to injury or death Safety grounding The PicoScope 3425 PC Oscilloscope connects directly to the ground of a computer through the USB cable provided This connection is intended only to minimise interfe...

Page 7: ... Part 15 of the FCC Rules These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment This equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with the instruction manual may cause harmful interference to radio communications Operation of this equipment in ...

Page 8: ... no two applications are the same Pico Technology cannot guarantee that its equipment or software is suitable for a given application It is your responsibility therefore to ensure that the product is suitable for your application Mission critical applications This software is intended for use on a computer that may be running other software products For this reason one of the conditions of the lic...

Page 9: ...ain technical assistance from Pico Technology at the following address Address Pico Technology James House Colmworth Business Park Eaton Socon St Neots PE19 8YG United Kingdom Phone 44 0 1480 396 395 Fax 44 0 1480 396 296 Email Technical Support support picotech com Sales sales picotech com Web site www picotech com ...

Page 10: ...h this oscilloscope you must ensure that they are rated for the voltage you are measuring 2 2 Installation instructions Important You must install the PicoScope software before connecting a PicoScope 3425 PC Oscilloscope to your PC for the first time Install the software by following the steps in the quick start guide supplied with your oscilloscope You can then connect your oscilloscope to the PC...

Page 11: ...haracteristics as Ch A 4 Ch D Input channel D Has the same characteristics as Ch A 5 Ground Can be used with the current clamp adaptor supplied to convert one or more of the differential inputs to single ended inputs Can also be used to ground the screen of the shielded twisted pair cable supplied The scope s ground is connected to the PC s ground through the USB cable You MUST NOT rely on the sco...

Page 12: ...ribed Most current clamps have an internal metal case that readily picks up electromagnetic noise from the environment and if the case were not grounded this noise would interfere with the signal TA039 Screened twisted pair cable Use this cable to connect a signal directly to the oscilloscope A positive signal will be displayed when you connect the red BNC plug to the more positive signal and the ...

Page 13: ... 400 V ranges Maximum safe voltages Differential Any input above scope GND 400 V 400 V 600 V transient Measurement category rating CAT I Voltage ranges 100 mV 200 mV 500 mV 1 V 2 V 5 V 10 V 20 V 50 V 100 V 200 V 400 V Accuracy Voltage 1 Time 50 ppm Linearity 12 bits Noise 10 LSB Operating environment Temperature range Humidity range 0 C to 40 C 20 C to 30 C for quoted accuracy Minimum 5 RH non con...

Page 14: ... reference to ground so you need to connect the scope s ground clip to the centre of the secondary You can then measure either VP or VN with respect to ground but not the total voltage across the secondary The diagram below shows a single ended scope connected between VP and ground With a differential oscilloscope you can directly measure the secondary voltage by connecting the positive probe to V...

Page 15: ...ltage the difference between the positive and negative inputs on each channel exceeds the selected voltage range This condition causes clipping of the displayed signal 2 8 AC DC coupling Each channel can be set to use either AC or DC coupling When AC coupling is used any DC component of the signal below about 1 hertz is filtered out To change the coupling mode select AC or DC from the control on t...

Page 16: ...e scope unit is ready Copy data to a buffer Stop capturing data Close the scope unit Numerous sample programs are installed with your PicoScope software These show how to use the functions of the driver software in each of the modes available 3 2 1 Voltage ranges It is possible to set the gain for each channel with the ps3000_set_channel function This will give an input voltage range between 100 m...

Page 17: ... size of the oscilloscope s memory A PicoScope 3425 can sample at a number of different rates These rates correspond to the maximum sampling rate divided by 1 2 4 8 and so on There is a separate memory buffer for each channel When a channel is unused its memory can be borrowed by the enabled channels This feature is handled transparently by the driver The driver normally performs a number of setup...

Page 18: ...uires fresh data on every transfer In windowed mode a fixed number of samples is returned where the oldest samples may have already been returned before Windowed mode is useful when the program requires a constant time period of data Once the oscilloscope is collecting data in streaming mode any setup changes for example changing a channel range or AC DC setting will cause a restart of the data st...

Page 19: ...ocedure for reading and displaying data in fast streaming mode 1 Open the oscilloscope using ps3000_open_unit 2 Select channel ranges and AC DC switches using ps3000_set_channel 3 Set the trigger using ps3000_set_trigger 4 Start the oscilloscope running using ps3000_run_streaming_ns 5 Get a block of data from the oscilloscope using ps3000_get_streaming_last_values 6 Display or process the data 7 I...

Page 20: ...f the signal Constant Reading Voltage PS3000_LOST_DATA 32 768 Indicates a buffer overrun in fast streaming mode PS3000_MIN_VALUE 32 767 Negative full scale 0 0 Zero volts PS3000_MAX_VALUE 32 767 Positive full scale 3 2 7 Combining oscilloscopes It is possible to collect data using up to four PicoScope 3000 Series PC Oscilloscopes at the same time Each oscilloscope must be connected to a separate U...

Page 21: ...dvTriggerChannelConditions ps3000SetAdvTriggerChannelDirections ps3000SetPulseWidthQualifier ps3000SetAdvTriggerDelay ps3000_run_block ps3000_run_streaming ps3000_ready ps3000_stop ps3000_get_values ps3000_get_times_and_values ps3000_run_streaming_ns ps3000_get_streaming_last_values ps3000_get_streaming_values ps3000_get_streaming_values_no_aggregation ps3000_save_streaming_data ps3000_overview_bu...

Page 22: ... 8 1 ps3000_open_unit short ps3000_open_unit void This function opens a PicoScope 3000 Series PC Oscilloscope The driver can support up to four oscilloscopes Applicability All modes Arguments None Returns 1 if the oscilloscope fails to open 0 if no oscilloscope is found 0 device handle if the device opened ...

Page 23: ...s PC Oscilloscope without waiting for the operation to finish You can find out when it has finished by periodically calling ps3000_open_unit_progress until that function returns a non zero value The driver can support up to four oscilloscopes Applicability All modes Arguments None Returns 0 if there is a previous open operation in progress 1 if the call has successfully initiated an open operation...

Page 24: ...h ps3000_open_unit_async Arguments handle a pointer to a location in which the function will store the handle of the opened device 0 if no unit is found or the unit fails to open handle of device valid only if function returns TRUE progress_percent a pointer to an estimate of the progress towards opening the unit from 0 to 100 100 implies that the operation is complete Returns 1 if the driver succ...

Page 25: ...aracter string buffer If the string is not long enough to accept all of the information only the first string_length characters are returned line an enumerated type specifying what information is required from the driver Returns The length of the string written to the character string buffer string by the function 0 if one of the parameters is out of range or a null pointer is passed for string li...

Page 26: ...numerated type Use PS3000_CHANNEL_A 0 or PS3000_CHANNEL_B 1 enabled specifies if the channel is active TRUE active FALSE inactive dc specifies the AC DC coupling mode TRUE DC FALSE AC range a code between 1 and 10 See the table below Returns 0 if unsuccessful or if one or more of the arguments are out of range 1 if successful Code Enumeration Range 3 PS3000_100MV 100 mV 4 PS3000_200MV 200 mV 5 PS3...

Page 27: ...te the most suitable time unit to use time_interval a pointer to the time interval in nanoseconds between readings at the selected timebase If a null pointer is passed nothing will be written here time_units a pointer to the most suitable units that the results should be measured in This value should also be passed when calling ps3000_get_times_and_values If a null pointer is passed nothing will b...

Page 28: ...s3425 en 3 2 8 7 ps3000_flash_led short ps3000_flash_led short handle Flashes the LED on the front of the oscilloscope three times and returns within one second Applicability All modes Arguments handle the handle of the required device Returns 1 if a valid handle is passed 0 if handle is invalid ...

Page 29: ...is scaled in 16 bit ADC counts at the currently selected range If an external trigger is enabled the range is fixed at 20V direction use PS3000_RISING 0 or PS3000_FALLING 1 delay specifies the delay as a percentage of the requested number of data points between the trigger event and the start of the block It should be in the range 100 to 100 Thus 0 means that the trigger event is at the first data...

Page 30: ...PS3000_NONE 5 threshold the threshold for the trigger event This is scaled in 16 bit ADC counts at the currently selected range If an external trigger is enabled the range is fixed at 20 V direction use PS3000_RISING 0 or PS3000_FALLING 1 delay specifies the delay as a percentage of the requested number of data points between the trigger event and the start of the block It should be in the range 1...

Page 31: ...ll modes Arguments handle the handle of the required device channelProperties a pointer to a TRIGGER_CHANNEL_PROPERTIES structure describing the requested properties If NULL triggering is switched off nChannelProperties should be set to 1 if channelProperties is non null otherwise 0 autoTriggerMilliseconds the time in milliseconds for which the scope device will wait before collecting data if no t...

Page 32: ...ODE thresholdMode TRIGGER_CHANNEL_PROPERTIES Applicability All modes Members thresholdMajor the upper threshold at which the trigger event is to take place This is scaled in 16 bit ADC counts at the currently selected range for that channel thresholdMinor the lower threshold at which the trigger event is to take place This is scaled in 16 bit ADC counts at the currently selected range for that cha...

Page 33: ...is set up by defining a TRIGGER_CONDITIONS structure Each structure is the AND of the states of one scope input Applicability All modes Arguments handle the handle of the required device conditions a pointer to a TRIGGER_CONDITIONS structure specifying the conditions that should be applied to the current trigger channel If NULL triggering is switched off nConditions should be set to 1 if condition...

Page 34: ...lseWidthQualifier TRIGGER_CONDITIONS Applicability All modes Members channelA channelB channelC channelD pulseWidthQualifier the type of condition that should be applied to each channel Use these constants CONDITION_DONT_CARE 0 CONDITION_TRUE 1 CONDITION_FALSE 2 external not used Remarks The channels that are set to CONDITION_TRUE or CONDITION_FALSE must all meet their conditions simultaneously to...

Page 35: ...rough the threshold to activate the trigger The allowable values for a THRESHOLD_DIRECTION variable are listed in the table below ext not used Returns 0 if unsuccessful or if one or more of the arguments are out of range 1 if successful THRESHOLD_DIRECTION constants ABOVE for gated triggers above a threshold BELOW for gated triggers below a threshold RISING for threshold triggers rising edge FALLI...

Page 36: ... structure specifying the conditions that should be applied to the trigger channel If conditions is NULL then the pulse width qualifier is not used nConditions should be set to 1 if conditions is non null otherwise 0 direction the direction of the signal required to trigger the pulse lower the lower limit of the pulse width counter upper the upper limit of the pulse width counter This parameter is...

Page 37: ...ualifier conditions and is defined as follows typedef struct tPwqConditions TRIGGER_STATE channelA TRIGGER_STATE channelB TRIGGER_STATE channelC TRIGGER_STATE channelD TRIGGER_STATE external PWQ_CONDITIONS Applicability Pulse width qualified triggering Members channelA channelB channelC channelD the type of condition that should be applied to each channel Use these constants CONDITION_DONT_CARE 0 ...

Page 38: ...d time after the trigger event Applicability All modes Arguments handle the handle of the required device delay specifies the delay as a percentage of the requested number of data points between the trigger event and the start of the block It should be in the range 100 to 100 For example 0 means that the trigger event is at the first data value in the block and 50 means that it is in the middle of...

Page 39: ... 1 selects a sample rate half as fast timebase 2 is half as fast again and so on For the maximum sample rate see the specifications Note that the number of channels enabled may affect the availability of the fastest timebases oversample the oversampling factor a number between 1 and 256 See Oversampling for details time_indisposed_ms a pointer to the approximate time in milliseconds over which the...

Page 40: ...e only Arguments handle the handle of the required device sample_interval_ms the time interval in milliseconds between data points This can be no shorter than 1 ms max_samples the maximum number of samples that the driver is to store This can be no greater than 60 000 It is the caller s responsibility to retrieve data before the oldest values are overwritten windowed if this is 0 only the values t...

Page 41: ...y Does nothing if the oscilloscope is in streaming mode Arguments handle the handle of the required device Returns 1 if ready The oscilloscope has collected a complete block of data or the auto trigger timeout has been reached 0 if not ready An invalid handle is passed or the oscilloscope is in streaming mode or the scope is still collecting data in block mode 1 if device not attached The endpoint...

Page 42: ...p short ps3000_stop short handle Call this function to stop the oscilloscope sampling data If this function is called before a trigger event occurs the oscilloscope may not contain valid data Applicability All modes Arguments handle the handle of the required device Returns 0 if an invalid handle is passed 1 if successful ...

Page 43: ...buffer_a buffer_b buffer_c buffer_d pointers to the buffers that receive data from the specified channels A B C or D A pointer is unused if the oscilloscope is not collecting data from that channel If a pointer is NULL nothing will be written to it overflow a bit pattern indicating whether an overflow has occurred on a channel Bit 0 is the least significant bit The bit assignments are as follows 1...

Page 44: ...to the buffers that receive data from the specified channels A B C or D A pointer is unused if the oscilloscope is not collecting data from that channel If a pointer is NULL nothing will be written to it overflow a bit pattern indicating whether an overflow has occurred on a channel Bit 0 is the LSB The bit assignments are as follows 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 D C B A D C B A common mod...

Page 45: ...amples the maximum number of samples that the driver should store from each channel Your computer must have enough physical memory for this many samples multiplied by the number of channels in use multiplied by the number of bytes per sample auto_stop a Boolean to indicate whether streaming should stop automatically when max_samples is reached Set to any non zero value for TRUE noOfSamplesPerAggre...

Page 46: ...g You must have called ps3000_run_streaming_ns beforehand to set up fast streaming Applicability Fast streaming mode only Arguments handle the handle of the required device lpGetOverviewBuffersMaxMin a pointer to the callback function in your application that receives data from the streaming driver Returns The actual number of data values returned per channel which may be less than max_samples if ...

Page 47: ... refers to it only by the address that you pass to ps3000_get_streaming_last_values For an example of a suitable callback function see the C sample code included in your PicoScope installation Applicability Fast streaming mode only Arguments overviewBuffers a pointer to a location where ps3000_get_streaming_last_values will store a pointer to its overview buffers that contain the sampled data The ...

Page 48: ...ode It allows you to retrieve data with different aggregation ratios and thus zoom in to and out of any region of the data Before calling this function first capture some data in fast streaming mode stop fast streaming by calling ps3000_stop then allocate sufficient buffer space to receive the requested data The function will store the data in your buffer with values in the range PS3000_MIN_VALUE ...

Page 49: ...t channels has overflowed 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 D C B A D C B A common mode overflow differential overflow triggerAt a pointer to where the function will write an index into the buffers The index is the number of the sample at the trigger reference point Valid only when triggered is TRUE triggered a pointer to a Boolean indicating that a trigger has occurred and triggerAt is valid ...

Page 50: ... not be collected because of a buffer overrun See Scaling for more details of data values Applicability Fast streaming mode only Arguments handle the handle of the required device start_time the time in nanoseconds of the first data sample required pbuffer_a pbuffer_b pbuffer_c pbuffer_d pointers to buffers into which the function will write the raw sample values from channels A B C and D overflow...

Page 51: ...l available streaming data to the my_save_streaming_data callback function in your application Your callback function decides what to do with the data Applicability Fast streaming mode only Arguments handle the handle of the required device lpCallbackFunc a pointer to the my_save_streaming_data callback function in your application that handles the saving of streaming data dataBuffers a pointer to...

Page 52: ...streaming_ns have overrun If an overrun occurs you can choose to increase the overview_buffer_size argument that you pass in the next call to ps3000_run_streaming_ns Applicability Fast streaming mode only Arguments handle the handle of the required device previous_buffer_overrun a pointer to a Boolean indicating whether the overview buffers have overrun Any non zero value indicates a buffer overru...

Page 53: ...save_streaming_data The function name my_save_streaming_data is just for illustration When you write this function you can give it any name you wish The PicoScope driver does not need to know your function s name it refers to it only by the address that you pass to ps3000_save_streaming_data Applicability Fast streaming mode only Arguments dataBuffer a pointer to the buffer where the values are st...

Page 54: ...eserved ps3425 en 3 2 8 29 ps3000_close_unit short ps3000_close_unit short handle Shuts down a PicoScope 3425 oscilloscope Applicability All modes Arguments handle the handle returned by ps3000_open_unit of the oscilloscope being closed Returns 1 if a valid handle is passed 0 if not 18 ...

Page 55: ...pWizard To compile the program create a new project for an Application containing the following files from the Examples ps3000 subdirectory of your PicoScope installation ps3000 c ps3000 rc and ps3000bc lib Borland 32 bit applications or ps3000 lib Microsoft Visual C 32 bit applications The following files must be in the compilation directory ps3000 rch ps3000 h and the following file must be in t...

Page 56: ...stsResource h rename to resource h before compiling You will also need the following library for Microsoft C ps3000 lib Microsoft Visual C 32 bit applications Ensure that the program directory contains a copy of ps3000 dll from the PicoScope installation directory A Visual Studio 2005 VC8 project file faststreaming vcproj is provided 3 3 3 Visual Basic The Examples ps3000 subdirectory of your Pico...

Page 57: ...isual Basic The functions which return a TRUE FALSE value return 0 for FALSE and 1 for TRUE whereas Visual Basic expects 65 535 for TRUE Check for 0 rather than TRUE 3 3 6 Agilent VEE The example function ps3000 vee is in the Examples ps3000 subdirectory of your PicoScope installation It uses procedures that are defined in ps3000 vh It was tested using Agilent VEE version 5 3 3 7 LabView The VI ex...

Page 58: ...e driver cannot allocate enough of the computer s memory to operate the oscilloscope Consult the system requirements section for more information 3 A PicoScope 3000 Series PC Oscilloscope could not be found on your machine Make sure the software is installed before the oscilloscope is plugged into the USB socket and restart your computer 4 5 or 6 There is a problem with the oscilloscope itself The...

Page 59: ...The oscilloscope is functioning correctly 1 PS3000_MAX_UNITS_OPENED Attempts have been made to open more than PS3000_MAX_UNITS 2 PS3000_MEM_FAIL Not enough memory could be allocated on the host machine 3 PS3000_NOT_FOUND An oscilloscope could not be found 4 PS3000_FW_FAIL Unable to download firmware 5 PS3000_NOT_RESPONDING The oscilloscope is not responding to commands from the PC 6 PS3000_CONFIG_...

Page 60: ...mplitude Block mode A sampling mode in which the computer prompts the oscilloscope to collect a block of data into its internal memory before stopping the oscilloscope and transferring the whole block into computer memory This mode of operation is effective when the input signal being sampled is high frequency Note To avoid aliasing effects the maximum input frequency must be less than half the sa...

Page 61: ... differential scope PicoScope software This is a software product that accompanies all our oscilloscopes It turns your PC into an oscilloscope spectrum analyser and meter display Signal generator This is a feature on an oscilloscope which allows a signal to be generated without an external input device being present The signal generator output is the BNC socket marked E on the oscilloscope If you ...

Page 62: ...s a standard port that enables you to connect external devices to PCs A typical USB 2 0 port supports a data transfer rate that is 40 times faster than that supported by USB 1 1 USB 2 0 is backwards compatible with USB 1 1 Vertical resolution A value in bits indicating the degree of precision with which the oscilloscope can turn input voltages into digital values Calculation techniques can improve...

Page 63: ... 55 E Electric shock risk 3 Email 5 EMC directive 89 336 EEC 3 EN61326 1 1997 Class B 3 Environmental conditions 9 Equipotentiality 3 Error codes 54 55 Excel macros 53 External trigger 12 25 26 F Fast streaming mode 15 Fax 5 FCC notice 3 Fitness for purpose 4 Functions 17 ps3000_close_unit 50 ps3000_flash_led 24 ps3000_get_streaming_last_values 42 ps3000_get_streaming_values 44 ps3000_get_streamin...

Page 64: ...oscope probe 7 8 Overflow indicator 11 Oversampling 16 Overview buffer 48 P Pack contents 6 PC connection 9 PC Oscilloscope 1 56 PC requirements 1 Pico Technical Support 54 PicoLog software 12 55 picopp inf 12 picopp sys 12 PicoScope 3000 Series 1 16 54 55 PicoScope software 1 6 12 55 56 common mode overflow indicator 11 overflow indicator 11 Power supply 9 Pre trigger 12 Programming C 51 C 52 Dep...

Page 65: ...e 12 Time interval 16 Timebase 23 35 56 Trademarks 4 TRIGGER_CHANNEL_PROPERTIES structure 28 TRIGGER_CONDITIONS structure 30 Triggering 12 25 26 U Upgrades 4 Usage 4 USB 1 9 56 cable 6 hub 16 port 54 V Vertical resolution 9 16 Viruses 4 Visual Basic programming 52 Voltage range 9 56 W Website 5 Weight 9 Windowed mode 14 ...

Page 66: ......

Page 67: ...63 Copyright 2007 Pico Technology Limited All rights reserved ps3425 en ...

Page 68: ...ames House Colmworth Business Park Eaton Socon St Neots PE19 8YG United Kingdom Tel 44 0 1480 396 395 Fax 44 0 1480 396 296 Web www picotech com Copyright 2007 Pico Technology Limited All rights reserved ps3425 en 2 7 12 07 ...

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