User Interface
Figure 1: User interface of the QPA200
All controls and signal terminations of the QPA200 are on the face of the instrument as illustrated in Figure 1. The AC power cord receptacle is at the rear. At the left are three multi-colored LED indicators that alert the user to the instrument status. When the power switch is closed and the amplifier is on, the green LED marked power will be illuminated. The red LED marked current is illuminated when the amplifier output current has exceeded the +/-200mA threshold.
The yellow LED marked temp is illuminated to signify that a fault has occurred and the instrument has entered the thermal shut-down mode. This latter feature is discussed later.
Input and output signals of the QPA200 are available via four BNC connectors. The analog input signal should be connected to the terminal marked input while the output signal leading to the piezo load should be connected to the terminal marked output. Note that the output of the QPA200 contains hazardous voltage levels that can easily damage electronic equipment or cause lethal injury to the user. Extreme caution should be exercised when operating the QPA200. Loads should be connected and disconnected to the output terminal only when power is off.
Gain Adjust
The QPA200 offers the user a selection of either fixed or adjustable gain. Gain control is implemented by the switch and knob controls at the center of the instrument. The gain switch can be placed in one of three positions. When the switch is raised high in the fix position, the gain of the QPA200 is fixed at 50V/V. When the switch is lowered to the adj position, the gain of the QPA200 is variable in the range of 10 to 100V/V and is controlled by the knob marked Gain Adj. When the switch is in the middle position, the output voltage is driven to zero volts. Note that this latter case does not disconnect the output of the amplifier nor put it in a high-impedance state.
