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The Constant Current or Constant Voltage Isolated Linear Stimulator (STMISOL) will connect to any analog output signal drive (±10 V input) and has two functional modes:
- Voltage and current stimulator (unipolar or bipolar)—the STMISOL connects directly to the STM100C (50
 output port) or the UIM100C (Analog Output 0 or 1 port) associated with the MP1X0 system.
- Linear stimulator—the STMISOL can be used to generate stimulation signals that can have arbitrary waveshape (not compatible with MP36/35). Typically, stimulators can only generate simple unipolar or bipolar pulses. The STMISOL, however, can output unipolar or bipolar arbitrary waves such as pulse (single or train), square, sine, triangle, exponentially decaying, modulated envelopes, and fully user-specified types.
The STMISOL can output either voltage or current waveforms.
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Voltage (V) mode—the STMISOL multiplies the Control Input Voltage by a factor of 20, to present that amplified signal at the STMISOL output.
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Current (I) mode—the STMISOL multiplies the Control Voltage by a factor of (10 ma/V) to present that associated output current at the STMISOL output.
Isolation characteristics—The STMISOL isolates the Control Input Voltage signal from the stimulus output to 1500 VDC HiPot and approximately 90 pF of coupling capacitance.
This very high degree of input/output isolation helps ensure subject safety and helps considerably to substantially reduce, or eliminate, stimulus artifact.
Stimulus artifact results when some percentage of electrical current from the stimulation site is directed to the recording site due to electrical leakage paths intrinsic to the stimulation/recording equipment. In the case of the STMISOL, the leakage conductances and capacitances that permit this artifact to occur are reduced to extremely small values.
Power ON Safety—When you Power ON the STMISOL, you must also hold Reset for at least 3 seconds. This forces the unit into an "operational but no output state" and protects the subject if accidentally connected to electrodes on power-up.
Applications  Biomechanics EMG Electromyography Exercise Physiology fNIR Functional Near Infrared Optical Brain Imaging
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STMISOL Specifications
Control Voltage: ±10 V maximum input
Control Voltage Interface: Male 3.5 mm mono phone plug
Isolation
Control Voltage GND to Isolated Output GND: 90 pF at 1500 VDC HiPot
Output Stimulation
Voltage (V) Mode: ±200 V with ±100 ma compliance;
Output Impedance = 100
Current (I) Mode: ±100 ma with ±200 V compliance;
Output Impedance - 1 G
Input to Output Ratio
Voltage (V) Mode: ±10 V DC input creates output of ±200 VDC (1:20 ratio - V/V)
Current (I) Mode: ±10 V DC input creates output of ±100 mA (1:10 ratio - V/ma)
Timing
Voltage Rise time: 200 V in 9.5 µsec (T10-T90)
Current Rise Time: 100 ma in 9.5 µsec (T10-T90)
Max pulse width: 100 msec
Max sine frequency: 30 kHz (-3 dB)
Input Control Voltage
Physical Interface: 3.5mm male mono phone plug
Compatibility: MP: UIM100C (Analog Out 0 or 1), STM100C (50 )
3rd-party: signal generator with ±10 V output range
Noise — also referred to as Standard Deviation
Very low, about +/-0.02% of Full Scale Range (FSR)
- current output: accuracy to voltage input is within +/- 2%, FSR is +/-100mA
- linearity is +/- 0.1%
Protection
Wave (pulse) Duration:
Output or current compliance voltage (Vout): Vout (magnitude) < 100V
- fully arbitrary, no limit to wave (pulse) duration
Output or current compliance voltage (Vout): Vout (magnitude) > 100V
- 100 msec typical (limiting to 20 ms at 100 ma current drive)
Current Limiting: ±350 ma ‹(short circuit)
Voltage Limiting: ±210 V ‹nominal
Reset Push Button: Required with each power ON ‹in for 3 seconds to Reset
Manual Test
Voltage Output Pulse: 100 V for 2 msec
Current Output Pulse: 50 ma for 2 msec
Output Indicator: ON for P-P amplitudes > 1% FSR
Fuse: 2 amp fast blow
Power Adapter: 12 VDC at 1 amp (AC100A)
Important Notes
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A) In Current (I) Mode stimulation, if the output has a load (typically high impedance) that induces railing for the specific output current, then the STMISOL will immediately go into "Protect" mode. In the case of an unloaded output, this state will happen as soon as the STMISOL is placed into Current (I) Mode stimulation. This happens because an "unloaded" STMISOL output simply means that an arbitrarily high resistance load is attached to the STMISOL. To correctly operate in Current (I) Mode stimulation:
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Place the proper load between the stimulation electrodes, and
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Press the"Reset" pushbutton for 3 seconds to activate the unit.
- B) In either stimulation mode (V or I), the output level (OL) will directly be a function of the applied Control Input Voltage (CIV). The conversion ratios are as follows:
Voltage (V) Mode: CIV (volts)*20 (volts/volts) = OL (volts)
Current (I) Mode: CIV (volts)*10 (ma/volts) = OL (ma)
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C) In order to be sensitive to output waveform presence, the output waveform indicator—red LED just above BNC output connector —will glow very slightly. Waveform output indication can be observed as an increasing intensity of this red LED. The output waveform indicator is designed to provde a visual indication of output, even if wave duration is extremely short, so it may show a waveform output for some brief period of time after the output wave has already passed.
Safety Notes
- Never place the stimulation electrodes so that it’s possible for stimulation current to pass through the subject’s heart. This can happen if electrodes are placed so that the leads “straddle” to the left and right sides of the subject’s body. Place the stimulation electrodes close together on the SAME (left or right) side of the subject’s body appendage. Only place stimulation electrodes so they are on the appendage of interest. For example, for left leg stimulation, only place stimulation electrodes on the left leg and on NO other location on the body.
- Do not power ON or OFF the STMISOL unit while electrodes attached to the subject. Always be sure to place the STMISOL in VOLTAGE mode, with zero volts applied to input, before attaching/removing electrodes to/from the subject. Zero volts is automatically applied to the STMISOL input if the STMISOL input cable is unplugged from any signal source.
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It is ideal to use the STM100C for stimulation control, because it permits manual control of the stimulation level. To use the STM100C:
• Plug the Control Input Voltage line for the STMISOL into the 50 ohm output of the STM100C.
• Before stimulation begins, turn the Output Level Control knob to 0%.
• Initiate stimulation in the AcqKnowledge software (see Application Note AH162).
• After stimulation is initiated, slowly turn the STM100C Output Level Control to the desired level.
• When the stimulation session is ended, turn the STM100C Output Level Control back to 0%.
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Do not remove electrodes while in current (I) mode; it’s possible for subjects to receive a shock if they remove electrodes while the STMISOL is in current (I) mode because the STMISOL responds to the impedance increase and causes the current source to swing to a positive or negative rail.
Operating Procedure
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