The Universal Single Ended Amplifier (USEA) is a two stage non-inverting amplifier, voltage input to voltage output. It is optimized for amplification of low-level DC signals from transducers. Two internal jumper blocks that allow the user to select any one of ten gain settings ranging from X2 to X1500.
Fixed Gain Settings (user selectable): 2,5,10,15,20,50,100,150,200,500,1000,1500
Other gain settings are available on special order. An internal adjustment allows calibration to intermediate settings, either at the factory or by the end user. The USEA features a CAZ (Commutating Auto Zeroing) operational amplifier to achieve input offset voltage of typically 5 microvolts, and high accuracy, for amplification of small signals. The amplifier is designed for use with thermopile light sensors, O2 sensors, or any sensor that produces a small voltage that must be amplified to a higher level for interface to a data logger or control system. An option that can be installed at the factory is provision for an offset from zero, for sensors such as Net Radiometers that produce bipolar signals.
The
USEA provides a simple interface from low-level sensors to voltage
input data loggers, chart recorders, HVAC, and control systems. The
calibration for the sensor, in conjunction with the gain setting of
the USEA, can be used to compute in the equipment to compute the
instantaneous signal level with a high degree of accuracy.
On the USEA shown in the photo, the input cable from the sensor will enter through the gland nut to the left, and the output cable to the equipment will exit through the gland nut on the right. The USEA is also available with a BNC connector on the input. The calibration label on the outside of the enclousure is marked with the applicable gain setting. Wiring instructions and calibration notes are included with each unit.
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In order to convert the USEA's output voltage into the appropriate units, you will need the calibration information for the sensor you wish to connect to the input. Knowing the voltage output of the USEA, you can divide by the USEA gain setting to find the voltage being produced by the sensor itself. Then you multiply that voltage times the sensor calibration factor. Here are examples of the sensors that can be input to the USEA:
Eppley model PIR
Eppley model PYR
Novalynx net radiometer
Novalynx oxygen
Kipp&Zonen net radiometer, pyranometer
The USEA should be used with a filtered DC power supply of 18 volts or less. The current consumption of the USEA is approximately 2 milliamp. The power supply voltage must always exceed the maximum expected signal output voltage of the USEA by 2 Volts. This will ensure the USEA will have enough over-head to accommodate signal peaks. For example, an amplifier that must produce a full scale output of zero to 5 volts should be powered with a voltage of at least 7 volts, but no more than 18 volts.
The gain of the amplifier is set by positioning two jumpers as shown in the table and on the figure below. These set the gain of the two amplification stages in the USEA. The overall gain is the product of the two single-stage gains. The first stage gain has three possible settings: 2, 20, or 200. The second stage gain has four possible settings: 1, 2.5, 5, or 7.5. Refer to the table to find the particular setting required for your application:
second stage gain setting:
Gain=1X Gain=2.5X Gain=5X Gain=7.5X
first: ;---------------------------------------------
Gain=2X | 2X 5X 10X 15X
Gain=20X | 20X 50X 100X 150X
Gain=200X | 200X 500X 1000X 1500X
overall gain
When you order a specific gain setting from the factory, it will come to you with that setting preconfigured on the jumpers and with the gain specifically calibrated at that setting to within 0.1%.
You can move the jumpers to other settings, and the resulting gain will match the above ideal values to within 1%.
If you have an appropriat calibration equipment you can readjust the gain by following instructions in the manual. Intermediate values of gain can be had by adjusting the trimming poteniometer on the USEA circuit board. Changing the setting of this potentiometer multiplies all the gains in the above table above by the same factor. To carry out this adustment, you need a reference source for input to the amplifier, and an accurate voltmeter to measure the output.
There is a three-terminal connection block for the output, and a two terminal block for the input. The terminals on the USEA are color coded. The red terminal on the block of three is for positive power supply. The black terminal is for power supply ground/common. The green terminal on the block of three is the USEA's signal output. This should connect to the input of your logger or meter. The signal return reference point on the USEA is also the power supply common, so be sure that your logger or meter and the power supply do share the same ground, or strap the (-) input of a differential input over to common.
The USEA input is the block of two terminals, colored black and white. The input signal should be connected to the white terminal and the input signal ground should be connected to the black terminal. If the input device requires power it may be possible to supply it from the USEA's red power supply terminal. The two black terminals are connected together internally. The input of the amplifier is protected with a 5 volt zener diode and a 100� resistor.. Do not reverse the input connections or exceed 5 volts at the input.
Alternatively, the USEA-BNC uses a BNC connector. The positive signal must be on the center conductor.
When the offset is used, a small voltage appears in series with the negative leg of the input. This allows the USEA to amplify signals from instruments that produce both positive and negative voltages. For example, a net radiometer may produce a positive voltage during the day, and a negative voltage at night when the net radiation is outward from the earth. When this option is ordered, a second potentiometer adjustment on the USEA allows setting the small offset voltage applied to the negative leg of the sensor. In practice with a typical thermopile net radiometer, this offset may be set ton the order of 10 to 100 millivolts.
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