Model 3820
Universal Counter

Model 3820 Universal Counter

The Model 3820 Universal Counter allows up to eight measurement outputs to be generated as a function of time, these being:

Frequency
Average period
Average duty cycle
Average pulse-high time
Average pulse-low time
Event counts
Logic level (input voltage above/below threshold)
Time

The counter is principally intended for counting bi-level signals, which have two distinct voltage levels and clean transitions between them. Such signals include those generated by all common logic families used in electronic circuits, as well as most Trigger or Sync outputs of common test instruments. Measurements are updated at one of five user selectable intervals in the range 5 ms to 100 ms. the module is powered and controlled directly from the PC’s USB port, so requires no additional power source. Operation is entirely via software, with no manual switches or settings.

Two inputs are provided, each connected to a separate discriminator with adjustable threshold in the range –0.2 V to +0.5 V (–2.0 V to +5.0 V when used with a x10 probe). Following the discriminators, a multiplexer selects one of the signals for processing, allowing two different signals to be measured sequentially.

The supplied instrument control software consists of two layers. At the upper level, a simple Windows dialog application, "SR3820Counter", offers a convenient panel that allows the input (A, B or one of three internal test sources) to be selected, an update rate to be specified and all eight output measurements to be displayed. A further display area shows one of the measurements in a larger font size, as well as displaying a graphical trendline display.	Easy to use SR3820Counter applications software
Log measured data to file	The program also supports data logging to text file of the output measurements, with data being written directly in CSV (comma separated value) format for easy import to other programs. The software includes a sub menu where the voltage input thresholds can be set for the two inputs.
At the lower level, a dedicated ActiveX control known as "SR3820Comms" takes care of all communications to and from the instrument. Two main modes of operation are therefore possible. Users who simply want to operate the counter "out of the box" need do no more than plug it in, install the driver and software, and then use the SR3820 Universal Counter software to control it. Alternatively, when the counter is to be used as part of a computer controlled test system, then the user can develop software to control it via the SR3820Comms ActiveX control. The control eliminates the need for users to write the low-level code needed to send commands to and receive responses from the counter, allowing them to concentrate on developing the higher level program to run their experiments. Typical applications include: Photon counting Frequency measurement Test and measurement systems implement in LabVIEW where a *SIGNAL RECOVERY* 3820 counter can be used at the same time as instruments from different suppliers. Measurement system using scripted web pages (HTML files) operated via Internet Explorer.

The SR3820Comms control can of course also be used at the same time as other SIGNAL RECOVERY software ActiveX controls, such as SR3830Comms, allowing sophisticated systems to be assembled. For example, five APD's (avalanche photodiodes) could each be connected to the inputs of a model 3830 multiplexer, with the output being in turn connected to the A input of a model 3820 counter. Using both controls a user-developed application program could sequentially count the pulses being generated by each APD.

Both the top level SR3820 Universal Counter software and the lower-level SR3820Comms ActiveX control include comprehensive on-screen help files, while examples of how to use the control in LabVIEW, Visual Basic, VBScript, Visual C++ and Excel are also supplied.

3820 Software Linked to Excel Workbook
Sample Excel Workbook using SR3820Comms

Specifications

Input
	Impedance	1 MW, DC coupled
	Threshold
	Direct	–0.2 V to 0.5 V in 1 mV steps
	With x10 probe	–2 V to 5 V in 10 mV steps
	Polarity	Event counter triggers on rising edge of signal
	Sensitivity
	Direct	-15 dBm/50 W (23 mV rms) at 100 MHz, -10 dBm/50 W (0.7 V rms) at 120 MHz
	With x10 probe	1 V pk-pk sinewave at 125 MHz
	Min Input Slew Rate
	Direct	200 mV/µs
	With x10 probe	2 V/µs
	Abs. Max Input	< 50 V DC
Frequency Range		DC to 125 MHz min, 160 MHz typical
Timebase Accuracy		better than 5 ppm/degree C, 0 to 50 degrees C
Reporting Intervals		100, 50, 25, 10 and 5 ms
Functions
	Frequency	0 to 125 MHz
	Avg Period	> 8 ns
	Avg Duty Cycle	0 to 100%. Measured by sampling with a 65 MHz clock.
	Avg Pulse High or Low Time	> 5ns. Computed from Duty Cycle and Frequency
	Events	0 to 9,999,999,999 counts
	Logic Probe	0 = input voltage below threshold, 1 = input voltage above threshold
Indicators
	USB	Front-panel LED turns on during USB communications
	EVENT	Front-panel LED turns on when the input signal is above the threshold
USB Connector		Rear-panel, female USB connector for connection to the PC or a USB hub
USB Cable		Supplied complete with 6ft (1.8m) USB A/B cable
General
	Power Requirements	<500 mA @ +5 V DC, supplied via USB
	Dimensions
	Width	5½" (134 mm)
	Depth	4½" (114 mm)
	Height	1¼" (32 mm)
	Weight	9.9 oz (280 g)
Software	A CD containing the full applications package for Windows 98/2000/XP allowing threshold and input to be adjusted, and measurements to be displayed and saved is supplied with each unit. SR3820Comms ActiveX control also included for use with compatible programming languages, and examples provided of its use in C++, VisualBasic, VBScript, LabVIEW and Excel. Both top-level and ActiveX software includes on-screen help.

Already using a model 3820?
The model 3820 previously carried the SENSE-ations brand name. The hardware is unchanged from units carrying this older name, but the SR3820 Universal Counter software and SR3820Comms ActiveX control software are both new.

Software supplied with the SENSE-ations branded product included a program called PELauncher that was installed within the Startup programs group, as well as an ActiveX control (UCounterX) and application program (UCounter.exe). The PELauncher program was started when the computer booted and then ran in the background, monitoring USB bus activity. When a model 3820 Counter was plugged in the launcher program then started the UCounter.exe application software.

This approach is no longer used and the new SR3820 Universal Counter software is started in the same way as most other programs simply by clicking on the icon in the Start Programs menu. The SR3820Comms control is installed and registered during software installation and hence is available both to the SR3820 Universal Counter software and to user-written programs.

The new SR3820 Universal Counter application software generates data logging files that are compatible with those created by the older package, so in most cases users of the older software will get better performance by completely uninstalling it and replacing it with the new programs, which are available free of charge by clicking the link below.

Download Software
The SR3820Counter, SR3820Comms ActiveX control, and sample files are available by download from this website

Product support and upgrades are automatic and free of charge to existing users of the model 3820 Universal Counter. If you have already purchased the product and installed the software then you can simply download and install any later software version by clicking the link below.

To check if you need to upgrade, see the product version number on the distribution CD or in the program's "About" box and verify if this matches the version given below. If it is a lower number then you should upgrade.

Current Version Number:	2.00	Download SR3820 Counter Software
Date:	13th October 2004	Download SR3820 Counter Software

SIGNAL RECOVERY is part of Advanced Measurement Technology, Inc, a division of AMETEK, Inc.
It includes the businesses formerly trading as EG&G Instruments (Signal Recovery),
EG&G Signal Recovery and PerkinElmer Instruments (Signal Recovery)

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