Stimulus Isolator model IS4

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Caitlin Stevenson
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1 Stimulus Isolator model IS4

2 Stimulator Basics / Theory of Operation The IS4 Stimulator is a user controllable current source. Direct current can be generated over a range of several decades (from a few µas to maximally 10mA). Power for control and stimulation is supplied by batteries. The battery supply voltage is nominally 108V. This allows operation over a wide range of resistance. The product of applied current and resistance of the target device cannot exceed 100V (U=R*I). Assuming that a stimulation current of 1 ma is required, the resistance of the device must be less than 100kOhms. In case the device does not meet this condition (if the electrode resistance is too large) an internal buzzer is activated. The same applies for an open output (no connection to electrodes). The buzzer can be muted by pressing the power button. The buzzer is reactivated at the next turn on.

Controls on the front panel: MODE Switch POWER Push Button CURRENT RANGE Selector DECIMAL CURR Adjust POWER MONITOR Light TTL IN Connector BATTERY LOW Inicator Light Output POLARITY Switch OUTPUT

3 Controls on the front panel: MODE Switch POWER Push Button CURRENT RANGE Selector DECIMAL CURR Adjust POWER MONITOR Light TTL IN Connector BATTERY LOW Inicator Light Output POLARITY Switch OUTPUT Connectors Description of each Control MODE SWITCH This switch should be in the OFF position before tweaking any other knobs. In the OFF position no signal is present at the output unless a positive gate is applied to the TTL INPUT. To suppress inputsignals on the TTL IN, switch mode to DISABLED (topmost indication). By toggling the switch down a momentary PULSE can be generated manually. POWER PUSHBUTTON / BATTERY MANAGEMENT A single push turns the battery powered isolate stimulator ON, which is indicated by the topmost light (a red flashing powersaving Light Emitting Diode). A further push turns it OFF. Since the stimulator is driven by batteries, an automatic turn off function has been added. This means that the IS4 shuts down 2 hour after the last applied trigger (pulse generation internal or external) has occurred to avoid battery rundown. The IS4 Stimulator runs on two separate supply voltages. A 6V supply powers the control circuitry (consisting of four 1.5V UM3 type batteries) and a 108V high voltage supply (consisting of twelve 9V blocks) enables the device to provide large currents through a fairly high resistance. Both supplies are monitored by the internal microprocessor. Battery rundown is indicated on the respective LEDs. In case of LOW BATTERY (flashing 6V or

4 108V LED) of either supply, the unit should be returned immediately for maintenance. Dead batteries may leak, thereby damaging the circuitry. CURRENT RANGE SELECTOR This three position rotary switch determines the current range for stimulation (100mA, 1mA or 10mA) indicated as PER MIL OF RANGE. DECIMAL CURRENT ADJUST (PER MIL OF RANGE) In combination with the range selector it is possible to generate any value of current between 0.1µA and 10mA (1mA=1000µA). The values adjusted with the decimal current control are per mils of the preselected current range. Examples: Desired Current Current Range Selector Decimal Current Adjust 10µA 100µA µA 1mA µA 10mA 50 2mA 10mA 200 TTL IN BNC Connector This optical coupled input permits the device to be triggered by an external source e.g. a computer controlled I/O device. Any device that can deliver a 5V TTL 5mA is suitable. Current is on as long the input is high. For switching times and the input circuit diagram refer to technical specifications. CURRENT MONITOR LAMPS See Power Pushbutton. POLARITY SWITCH This has two positions. Normally stimulation is with the switch pushed down (+RED position). This means that the red output connector is more positive (hot) than the black and current is flowing (technical direction) from red to black. To work in the opposite direction the switch should be positioned to RED, which makes the black output connector more positive. OUTPUT CONNECTORS

5 For best results, short low capacity cables should be used to bring current to the target.

6 Instructions for optimal use: Operating principle: Fig: 1 Operation amplifier, transistor and shunt-resistor generates a voltage-controlled current sink. Independent of the load, the current will not be higher than: For a wide operation range the battery voltage has to be as high as practically possible. But large battery packs are associated with other problems. Usually this is in the range of 84V to 150V. In the working environment there are numerous potential sources of parasitic capacity, which affect rise and fall time. Fig. 2 Stray capacitance The user has the opportunity to suppress stray capacitance to a minimum by appropriate handling of the stimulus isolator device and correct attachment of cables. C1: capacitance between the box and the environment ground depends on the location of the isolation unit. A device directly placed on a metal table has more capacitance to ground. C2: capacitance between the transistor output (-) and ground depends on the wiring to the electrode (load). Connecting cables should be kept short and away from metals. CL: electrode and wire capacitance, depends on cable length, type and electrode size.

7 Specifications: Opto-isolation Input voltage for turn on = 3.9V or 3mA Input to output capacity 3.5pF Output to environment capacity, device on a grounded metal table 14pF Fast, 28µsec rise time (@ 60µA, 1Mohm) Expandable, current setting from PC possible Excellent linearity of response (see fig. 4) High linearity, error < 1% (100uA), respectively < 0.1% (10mA) Current remains constant with changing load resistance Low leak current < 5nA Auto Power off, prolongs battery life Battery life > 600h Battery monitoring Exact reproduction of current settings Dimension: 18.8 x 10.0 x 11.0 cm Weight: 1260g Accuracy in the 1mA Range (offset error): Current Error (1mA Range) Fig Current Error [ua] ua

8 Nonlinearity error in the 1mA range Non Liniearity Error 1mA Range Fig Liniarity Error [%] ua Comparison with other stimulus isolators: In comparison with other stimulus isolators, the IS4 has lower battery consumption. Switching time is comparable or better than other units and no adaptation occurs after the first stimulus pulse. Other Stimulus Isolator manufacturers: Word Precision Instruments A.M.P.I Digitimeter Coulbourn Instruments Geneq BAK Electronic Grass Getting Instruments BIOPAC Systems

9 PowerLab

NL800A - Stimulus Isolator

NL800A - Stimulus Isolator Introduction The NL800A STIMULUS ISOLATOR is a battery powered, opto-coupled isolator. It has a constant current output, with very high output impedance, making it suitable for