OCEAN CONTROLS KTA-200 User manual

KTA-200 Dual Amplifier / Attenuator
Dual DC Amplifier / Attenuator
•Dual op-amp board
•Each can be configured for Amplification or Attenuation (voltage divider)
•Single or Dual voltage supply
•Gain from 0. to 0.7 or .5 to 0
Often you want a simple amplifier to amplify or attenuate the signal you are feeding into a data acquisition system.
For example you have a signal from a temperature sensor that is providing 0mV/deg but you are only operating
over 0-40 degrees giving an effective span of 0 to 0.4V. Your data acquisition system accepts a signal of 0 to 0V
so you would like to amplify your signal by 0 to get better resolution.
Or you may have a 48V battery that you wish to monitor with a data acquisition system that has a 0 to 5V input
range. You could use a simple voltage divider but the input impedance of the data acquisition is only a few kilo-
ohm.
Or you may have a 4-20mA signal you wish to convert to 2 to 0V or to 5V
This Dual DC amplifier provides a solution to these problems and more
The dual DC amplifier circuit consists of two non inverting amplifiers (OP and OP2) with a voltage divider at the
input. The dual operational amplifier used is a Linear Technology LT 0 3 which features low offset voltage and can
be powered from a unipolar or bipolar supply.
Each amplifier is identical in design and is issued with one 50K potentiometer. Whether the circuit amplifies or
reduces the signal depends on where the 50K potentiometer is placed on the circuit. Because each amplifier is
identical we are only going to refer to the circuit using operational amplifier OP . If you place the pot in position P2
the circuit operates as an attenuator or voltage divider. If you place it position P it becomes a non inverting
amplifier.
Voltage Divider
If the potentiometer is fitted in position P2 then the combination of resistor R2 and P2 act as a voltage divider and
the operational amplifier is configured as a voltage follower with a gain of . This gives an effective gain of
P2/(R2+P2)
This will allow you to adjust the gain between 0.667 and 0. easily
Non Inverting Amplifier
If the potentiometer is fitted in position P then the combination of OP , R3 and P act as a non inverting amplifier.
Each amplifier has a variable gain feedback with the gain
+ R3/P
This will allow you to adjust the gain between .5 and 0 quite easily.
Filter
The effect of R3 and C3 is to provide a simple low pass filter to filter out high frequency noise. When the circuit is
operating as a Non Inverting amplifier the effect of high frequency noise is more pronounced.
Connecting 4-20mA ignals
If you wish to convert a 4-20mA signal to a voltage signal insert the 00 ohm resistor R . This will convert the 4-
20mA signal to a 0.4 to 2Volt signal. You can then adjust the Non Inverting Amplifier to the voltage span you
require.
Power upply
The circuit board can be supplied with a + 2 and - 2V or a + 5 and - 5V supply so that both positive and negative
signals can be amplified. The jumper should be placed in position J2.
If you are only interested in positive signals then the circuit can be supplied with a voltage from + 2V to +24VDC.
The jumper should be in position J .
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KTA-200 Dual Amplifier / Attenuator
Assembling the Kit
First solder in place all the resistors (leave out resistors R2 and R5 for voltage signals, solder them in for 4-20mA
signals) and terminals. Next solder in place all the capacitors noting the polarity of the electrolytic capacitors.
Solder in the diodes noting their polarity and finally solder in the 8 pin socket for the Operational Amplifier. Insert the
operational amplifier correctly into its socket.
If you want a gain of 0. to 0.667 solder the 50K potentiometer into P2 for op amp OP and P4 for op amp OP2
If you want a gain of .5 to 0 solder the 50K potentiometer into P for op amp OP and P3 for op amp OP2.
Before applying power put the jumper in position J for a unipolar power supply. Connect the positive side of the
supply to +Vs and the common of the supply to COM.
For a bipolar power supply put the jumper in position J2. Connect the positive side of the supply to +Vs, the
negative side of the supply to –Vs and the common to COM.
Calibrating the Amplifier for a Voltage ignal
Connect a V voltage source to I + and I - (I2+ and I2-). Turn on the power. Connect a multimeter to the output
O + and O - (O2+ and O2-). For a gain of .5 to 0 adjust the potentiometer P (P3) to the desired gain. For
example for a gain of 5 adjust the potentiometer until the multimeter reads 5V.
For a gain of 0. to 0.667 adjust the potentiometer P2 (P4) to the desired gain. For example for a gain of 0.5 adjust
the potentiometer until the multimeter reads 0.5V.
Repeat the same for the second operational amplifier.
Calibrating the Amplifier for a 4-20mA ignal
Connect a voltage source to I + and I - (I2+ and I2-). Monitor the current flowing into the +I with a multimeter and
adjust the voltage source to give a reading of 20mA. Connect a multimeter to the output O + and O - (O2+ and
O2-). For a gain of .5 to 0 adjust the potentiometer P (P3) to the desired gain. For a gain of 0. to 0.667 adjust
the potentiometer P2 (P4) to the desired gain.
Repeat the same for the other operational amplifier.
Parts List:
8-pin DIP socket (U )
Jumper
3 pin connector strip
3-way terminal blocks (T , T3-T4)
4 2-way terminal block (T2)
Semiconductors:
LT 0 3 Dual Op Amp
2 N4 48 silicon diode (D2)
Resistors:
2 00 ohm resistors
2 24K resistors
2 5 K resistors
2 50K 25 turn trimpots
Capacitors:
2 0. uF monolythic (C -C2)
2 0uF electrolytic (C3-C4)
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KTA-200 Dual Amplifier / Attenuator
Quick etup Notes:
Bipolar supply, put jumper in position J2
Single ended supply, put jumper in position J
Voltage signals, do not install R2 or R5
Current signals, install R2 or R5 accordingly
Amplification, install potentiometer in position P or P3
Attenuation (voltage divider), install potentiometer in position P2 or P4
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KTA-200
0: Amplifier / Attenuator Kit
: Dual Amplifier Assembled
2: Dual Attenuator Assembled
3: Amplifier / Attenuator Assembled
4: DIN Rail mount to suit
KIT: Supplied as kit, requires assembly
KTA: Assembled unit