General Description

The EMGA module Type 691 item number 731766 is a module for the HSE PLUGSYS measurement system. This amplifier serves for measuring and amplifying EMG signals. The input of this module incorporates an isolation amplifier in order to avoid hum interference. This provides isolation between the input circuit and the output circuit and housing. The isolation barrier is capable of withstanding voltages up to 300 Volt. The signal is indicated on a bar graph display. The frequency response of this module is arranged so that it can handle
EMG signals with frequencies up to 10kHz. The EMG signal is available as analogue voltage for recording at a BNC socket on the front panel and internally on the PLUGSYS system bus. A square-wave calibration generator with amplitudes of 0.3 mV and 1 mV is incorporated to calibrate the EMG amplitudes. Before the EMGA module can be used it has to be installed in a PLUGSYS housing Series 600

Installing the module in a housing

If you received your module installed in the housing you can skip this section. This is only for those who are adding this module to their existing PLUGSYS case.

Brief procedure:

• Pull out the mains plug on the housing.
• Remove the blank panel(s) at the housing slot position intended for the EMGA module.
• Prepare the module according to Section 4 (set lines and links).
• Insert the EMGA module, note the guide rails.
• Push the module firmly into the bus connector.
• Screw on the front panel.
• Plug in the EMG cable.
• Reconnect the mains plug to the housing.
• Switch on the housing.

Internal Instrument settings:

WARNING: the EMGA module must be protected against electrostatic discharges while it is outside the housing! The EMGA module contains highly sensitive MOS components which can be damaged or destroyed by  electrostatic discharges. If you dismantle the module or if you carry out any operations on the dismantled module you must ensure potential equilibration before touching any part of the printed circuit (by touching some grounded metal part, e.g. water tap, central heating radiator, grounded housing, PLUGSYS housing or similar).

Before you install the EMGA module into the PLUGSYS housing it is necessary to set a link on the circuit board so that the output signal is linked to the appropriate or required bus line. The module can only be used in conjunction with the complete system if the bus line has been connected up correctly.

NOTE: When selecting the bus line (AV1...16) be sure to use a free line and check this in the bus diagram. If there is no appropriate information in the bus diagram you can determine the bus line assignment only by removing all the modules and determining the signal paths selected on them using the corresponding operating instructions.

Find the position of the links from the diagram below.

Signal output for EMG to PLUGSYS bus system. Signal output for Envelope Integration to PLUGSYS bus system.

Fig. 2: Position of the internal links

In the example shown above the EMG signal output has been set so that the analogue EMG signal is on bus line AV 4. The Envelope Integration signal is on bus line AV 8.

Starting Up

After the EMG input cable has been connected to the input socket you can switch on the housing and start the measurement.

Setting the EMG Signal

The EMGA module incorporates a calibration generator for 0.3 mV and 1 mV; this can be switched on by moving the switch "0.3/MEAS/1" to the appropriate position. In the description below it is assumed that the instrument is switched on, ready for use, and connected to a data acquisition system. 

With the following you should use 1mV calibration settings.

The recording range can be adjusted so that it accurately fits the chart graduations. The procedure is as described below.

• Set switch "0.3/MEAS/1" to "MEAS".
• Short-circuit the three input electrodes.
• Set filter "HIGH CUT OFF" to 10 kHz.
• Set filter "LOW CUT OFF" to 2 Hz.
• Set "GAIN" switch to "x1" and switch "x1/x10/x100" to "x10".
• On the recorder set the pen with the position control to the center of the recording range.
• Move switch "0.3/MEAS/1" to "1 mV". The module now outputs a calibration signal with a 1 mV amplitude (from -0.5 mV to +0.5 mV). The shape of the signal depends on the filter setting. Set gain so that bar graph shows a deflection of about 75%
• Now adjust the recorder sensitivity so that the pen has a deflection of 4 cm (±2 cm around the zero line). Now 2 cm = 0.5 mV or 1 cm = 250 µV. The maximum deflection of ±4 cm corresponds to a voltage of ±1 mV.
• If the recorder does not have a fine sensitivity adjustment the PLUGSYS module ROM Type 670 can be used to attenuate the output signal of the EMG. Using a screwdriver you can reduce the output voltage by anticlockwise rotation on the appropriate channel.
• If you do not have a ROM you have to use a screwdriver to alter the "GAIN" potentiometer of the EMG amplifier to adjust the amplification so that you obtain the required 4 cm deflection.

After completing this procedure you have arranged the required scale on the recorder. If now you move the switch "0.3/MEAS/1" to its center position "MEAS" you can record the EMG.

As a check you can switch back occasionally to "1" or "0.3" and check the pen deflections. If you adjust the filter during the experiment you should check the calibration again and if necessary make a fine adjustment. If the EMG signal goes beyond the selected range you can move the switch "x0.5/x1/x2" to position "x0.5" and thereby halve the amplitude. If the EMG signal appears too small you can move the switch "x0.5/x1/x2" to position "x2" and thereby double the amplitude.

Please note:

Every alteration in the amplification on the "GAIN" switch or on the potentiometer also changes the calibration of the output amplitudes. The best way to avoid mistakes, after changing the amplification, consists of moving the switch "0.3/MEAS/1" to position "1" and to check the deflection which always corresponds to 1 mV.

Important: In position 1 mV the square-wave signal is output with 1 mV jumps. Due to the automatic return of the signal to the zero line (AC coupling) the square-wave signal jumps from -0.5 mV to +0.5 mV (amplitude 1 mV).

In position 0.3 mV a square-wave signal with 0.3 mV jumps is produced. Through the automatic return of the signal to the zero line (AC coupling) the square-wave signal then jumps from -0.15 mV to +0.15 mV (0.3 mV amplitude). 

The shape of the calibration signal alters with the filter setting "Low Filter cut off" the signal shown here applies only to the 2 Hz filter setting. 

Fig. 3: Setting up an EMG scale on the chart, selected range ±1mV

Example 2

With these details you should use the 1 mV calibration setting.

The recording range can be adjusted so that it accurately fits the chart graduations. The procedure is as described below.

• Set switch "0.3/MEAS/1" to "MEAS".
• Short-circuit the three input electrodes.
• Set filter "HIGH CUT OFF" to 10 kHz.
• Set filter "LOW CUT OFF" to 2 Hz.
• Set "GAIN" switch to "x1" and switch "x1/x10/x100" to "x10".
• On the recorder set the pen with the position control to the center of the recording range.
• Move switch "0.3/MEAS/1" to "1 mV". The module now outputs a calibration signal with a 1 mV amplitude (from -0.5 mV to +0.5 mV). The shape of the signal depends on the filter setting.
• Now adjust the recorder sensitivity so that the pen has a deflection of 8 cm (±4 cm around the
  zero line). Now 4 cm = 0.5 mV or 1 cm = 125 µV. The maximum deflection of ±4 cm now corresponds to
  a voltage of ±0.5 mV.
• If the recorder does not have a fine sensitivity adjustment the PLUGSYS module ROM Type 670 can be used to attenuate the output signal of the EMG. Using a screwdriver you can reduce the output voltage by anticlockwise rotation on the appropriate channel.
• If you do not have a ROM you have to use a screwdriver to alter the "GAIN" potentiometer of the
  EMG amplifier to adjust the amplification so that you obtain the required 8 cm deflection.

After completing this procedure you have arranged the required scale on the recorder. If now you move the switch "0.3/MEAS/1" to its center position "MEAS" you can record the EMG. As a check you can switch back occasionally to "1" or "0.3" and check the pen deflections. If you adjust the filter during the experiment you should check the calibration again and if necessary make a fine adjustment.

If the EMG signal goes beyond the selected range you can move the switch "x0.5/x1/x2" to position "x0.5" and thereby halve the amplitude. If the EMG signal appears too small you can move the switch "x0.5/x1/x2" to position "x2" and thereby double the amplitude.

Please Note:

Every alteration in the amplification on the "GAIN" switch or on the potentiometer also changes the calibration of the output amplitudes. The best way to avoid mistakes, after changing the amplification, consists of moving the switch "0.3/MEAS/1" to position "1" and to check the deflection which always corresponds to 1 mV. 

The shape of the calibration signal alters with the filter setting "LOW FILTER CUT OFF". The signal shown here applies only to the 2 Hz filter setting. 

Fig. 4: Setting up an EMG scale on the chart, selected range ±0.5mV, see text above.

Chart-Example with EMG Signal and Envelope Integration Signal

Fig. 5: Chart example. Channel 1 (TOP) EMG Signal. Channel 2 (Bottom) Envelope Integration Signal. Settings on EMGA: High Cut Off 10kHz, Low Cut Off 10 Hz, Leakage Time Constant (LTC) = 0.5s

Envelope Integration Signal with different settings of the LTC switch

Fig. 6: Chart example Channel 1 (Top) EMG Signal. Channel 2 (bottom) Envelope Integration Signal. Settings on EMGA: High Cut Off 10kHz, Low Cut Off 10 Hz. 

Input Pin Connections

The EMGA module has a 5-pin Binder input socket with screw lock for an HSE EMG input cable. Only pins 1, 2 and 3 are used. 

Description of the controls

Knob "FILTER HIGH CUT OFF" is used to set the upper frequency limit. This filter can be used to smooth the  recording traces. It is important, however, to ensure always that filtering does not change the amplitude. The adjustment is always made from the top downwards, i.e. always starting on 10 kHz, then switching down to 3 kHz and noting the amplitude. The amplitude should not be reduced, otherwise filtering is already too strong.

Knob "FILTER LOW CUT OFF" is used to set the lower frequency limit. This filter is used to set the time required by the signal to return to the isoelectric line (also known as AC coupling).

This is a fine adjustment of the amplification (GAIN) using a screwdriver. If the amplitude of the EMG signal is too large it can be reduced here. This fine adjustment is always linked to the switches "x0.5/x1/x2" and "x1/x10/x100". During setting up it is preferable to use the "x1" position so that with an amplitude decrease or increase it remains possible to halve (x0.5) or double (x2) the signal without recalibration. Switch "x1/x10/x100" is used to set the coarse gain in steps of 10.

Coarse amplification adjustment (GAIN) using the switch "x0.5/x1/x2". During setting up it is preferable to use the "x1" position so that with an amplitude decrease or increase it remains possible to halve (x0.5) or double (x2) the signal without recalibration.

Switch "x1/x10/x100" is used to set the coarse gain in steps of 10.

Switch "0.3/MEAS/1" to switch between calibration and measurement. The center position is the measurement position. In position "0.3" a calibration of 0.3 mV is simulated. AC coupling produces in this case a phasic signal with an amplitude of ±0.15 mV and the frequency of 3Hz (180 bpm) about the zero line. In position "1" a signal with an amplitude ±0.5 mV appears at the output. NOTE: after a change in the filter setting the calibration should be re-checked since a change in the filter may also influence the amplitude depending on the frequency of the EMG signal. 

Switch LTC (leakage time constant) for Envelope Integration. This switch is used to select between three leakage time constants for Envelope Integration. Envelope Integration means: the EMG signal is rectified, so that the negative waves appear on the positive side. This signal is Integrated with one of the time constants. The maxima of the integration signal results in the Envelope Signal.

BNC socket EMG OUT (±10 V). This socket carries the output signal in the voltage range ±10 V. This socket can be used for connection to a recorder or oscilloscope. 

BNC socket ENVELOPE INTEGRATION OUT (±10 V). This socket carries the Envelope Integration signal in the voltage range +10 V. This socket can be used for connection to a recorder or oscilloscope.

Isolated 5-pin input socket "EMG IN". The input circuit of the isolation amplifier can withstand voltages up to 300 Volt.

LED "OUT OF RANGE". This LED lights up as soon as the voltage range of ±10 V is exceeded. The amplification (GAIN) is then too high and has to be reduced at the "GAIN" fine control, at the switch "x0.5/x1/x2", or  "x1/x10/x100"

LED bar graph to visualize the EMG signal.

Troubleshooting

Technical Data

Mechanical Data