Many experiments in electrophysiology use a brief pulse of voltage or current as a stimulus to excite nerve or muscle cells.
Many experiments in electrophysiology use a brief voltage or current pulse to excite nerve or muscle cells. The voltage required to send this current through tissues can vary over a wide range. In addition, to minimize artifacts in the experimental results, it is desirable that the source of this E.M.F. should be isolated both from ground and from the timing generator used to release the stimulus.
The DS2A Constant Voltage and DS3 Constant Current isolated stimulators fulfill these requirements by using self contained batteries as the power source and optical coupling is employed to isolate the stimulator from the trigger source. Precise timing of stimulus application can be controlled by a PC or other generating device such as the DG2A Train Delay Generator.
The time duration of these stimulator's output is adjustable from 20 µs - 2 seconds via panel controls or via TTL pulses.
The DS2A has two output ranges with voltage maximums of 9V or 99V, and the DS3 has four overlapping decade ranges providing current maximums of 32 µA, 320 µA, 3.2 mA, and 32 mA. All ranges are continuously adjustable by a calibrated multi-turn output control and the polarity of the output can be reversed by a toggle switch.
Current is drawn from the batteries only when delivering an pulse, minimizing the drain on them. The maximum current drain is 30 mA plus the load current. These instruments have nonconductive enclosures and may be mounted on a metal mounting frame without connecting the internal circuitry to ground. A single shot button is provided which can be operated at all times irrespective of the trigger input status.
The visible difference between the two units (apart from the color) is that the output of the DS2A is defined in Volts while the output of the DS3 is defined in Amps. The actual stimulus passing through your preparation is measured in current in both cases and is dependent upon Ohms Law (V=IR).
If your preparation has a variable impedance (R) and you are using a constant voltage (V) source such as the DS2A, then the actual current (I) passing through the tissue may vary considerably between each stimulus, which may not be a good idea if you want to apply reproducible stimuli. With the DS3, the constant current circuitry prevents variations in the tissue or electrode impedance from altering the size of the applied current (within the 90 V compliance limit of the unit), leading to the stimulator equivalent of WYSIWYG – “What You Set Is What You Get”.
Unfortunately there are no well defined rules governing the circumstances under which stimulator should be used. Generally speaking, however, the constant voltage stimulator is more common in the literature.
|Maximum Voltage Output (DS2A)||99 V (High), 9 V (Low) selected by front panel switch; square wave pulse shape, typical rise time <1 µsec fall time < 3 µsec into resistive load|
|Current Output Ranges (DS3)||2 to 32 µA, 20 to 320 µA, 0.2 to 3.2 mA and 2 to 32 mA|
|Output Compliance (DS3)||90 V|
|Amplitude Control (DS2A & DS3)||Multi-turn dial provides continuous adjustment|
|Output Impedance (DS2A)||Dependent on position of amplitude control, 1.25 K max. at center position, 200 Ω at ends of travel|
|Overload (DS2A)||Automatic overload circuit prevents excessive output current being drawn by reducing output pulse width to less than 10 µsec when current of greater than 50 mA is detected|
|Pulse Width Controls (DS2A & DS3)||Two dials providing continuous adjustments over range 20 µsec to 2 sec, as well as selection of input pulse width|
|1)||6-Position Switch for pulse widths 10 µsec, 100 µsec, 1 msec, 10 msec, 100 msec with ± 10% accuracy or equal to input pulse width|
|2)||Multiplier continuously variable over range x2 to x20; pulse width is product of two dial settings|
|Trigger Requirements (DS2A & DS3)||Positive pulse of min. 3 V, max. 20 V amplitude required to trigger stimulator; trigger input current varies from 7 mA to 63 mA over above voltage range; trigger pulse width should not normally be less than 10 µsec|
|Trigger Isolation (DS2A & DS3)||Optical coupling is employed between trigger source and stimulator circuitry; capacity coupling less than 3 pF|
|Single Shot (DS2A & DS3)||Single shot push button provided|
|Normal/Reverse Switch (DS2A & DS3)||Normal||Red output terminal positive|
|Reverse||Red output terminal negative|
|Batteries||Self contained batteries are used to provide isolated source of power; current is drawn only when delivering output pulse; max. current drain is 30 mA plus load current|
|Battery Type||11 x PP3 - (IEC-6R61) style 9V batteries|
|Battery Test Sockets||Sockets provided on end of instrument case to allow batteries to be checked without removing|
|Output Terminals||Two 2 mm touch proof sockets fitted to front panel for output connections|
|Dimensions||Panel Size||190 x 110 mm (7.5 x 4.3 in)|
|Depth||80 mm (3.15 in) over knobs|
|Mounting||One or two model DS2A /DS3 stimulators may be mounted in 19 inch rack using D121-11 Mounting Frame|
|Weight||800 g (28.2 oz) with batteries installed|
|Order No.||Model No.||Product Description||USA Price||Order|
|65-0329||DS2A-MKII||Monopolar stimulator, constant voltage, isolated||Login||Login|
|65-0550||DS3||Monopolar stimulator, constant current, isolated||Login||Login|
|65-0337||D121-11||Rack mounting frame, 19 in, holds two DS2A/ DS3/ DG2||Login||Login|
|64-1425||CC-102||Cable, BNC + male banana to 1 mm jack (for use with field stimulation chambers)||Login||Login|
|Field Stimulation Chambers|
|64-0226||RC-21BRFS||Imaging chamber with field stimulation||Login||Login|
|64-0226U||RC-21BRFS||Imaging chamber with field stimulation - polysulfone body||Login||Login|
|64-0240R2||RC-27NE2||Narrow Bath Recording Chamber w/ Field Stimulation||Login||Login|
|64-0374||RC-47FSLP||Quick change chamber for 25 mm coverslips, with field stimulation||Login||Login|
|64-1725||RC-49MFSH||Magnetic Imaging / recording chamber with removable electrodes and heating elements||Login||Login|