QTech Q23, Owner'S Manual

Page: 37 / 50

TECHNICAL NOTES
Q23 Expansion Module Page 37
The op-amp is configured as a unity gain differential amplifier. Jumper J21 selects the input mode as follows:
❖
When J21 is open the circuit is configured for differential input mode. That is the negative Analog input line
is above ground therefore allowing for common mode input voltages up to 10 volts.
❖
When jumper J21 is closed the circuit is configured for single ended input mode. See page 35 for complete
details.
Note Each of the inputs to the differential Analog inputs are clamped with BAV99 high speed switching diodes to
both ground and +15 volts to keep the input voltage to op-amp in the range 0 to +15 volts. Differential and
common mode Analog input voltages outside 0 to +15 volts will cause the clamping diodes to conduct and
draw current from the Analog input source. The BAV99 diodes are rated at 200mA forward current.
Therefore care must be taken to ensure that over-voltage/under-voltage Analog input currents do not
exceed 200mA.
Analog Outputs
The Q23 Module has 2 Analog output channels. These are available at a 9 way connector labelled
‘ANALOG I/O’
on the front panel of the Q23 Module. The Analog output channels are numbered 5 & 6. The terminal labelled
‘G’
and is a system ground connection. The terminals labelled
‘+’
are connected to the switched positive rail of the
module’s power supply. The 2 Analog output channel have an associated yellow channel status LED to show the
state of the associated Analog output channel.
Note Analog channels 5 & 6 can be configured individually as either input or output channels.
Each Analog output channels yellow status LED shows the following channel status:
OFF Indicates that the Analog output is at 0V/0mA dependent upon the output mode configured. Or
less than 4mA in 4 to 20mA current output mode. That is the DAC count value is zero.
ON Indicates that the Analog output is within the specified voltage or current range dependent upon
the output mode configured. That is the DAC value is between 1 and 1022 counts.
FLASHING Indicates that the Analog output is at full-scale output of 5V/10V/20mA dependent upon the output
mode configured. That is the DAC count value is equal to 1023, i.e. maximum count.
The 2 Analog output channels can each be individually configured as single ended voltage or current outputs.
The diagram below shows the single ended Analog output circuit. The circuit includes PWM input preconditioning,
low impedance 5V/10V voltage output circuit and a voltage to current converter.
Circuit details of Single Ended Analog Output Channel.
The following paragraphs describe the various single ended Analog output configurations:
0 to 5V In this configuration jumper J1 is left open and jumper J3 has pins 2 & 3 closed. The op-amp U3A
operates as a unity gain amplifier. Q2 provides low impedance output drive.
0 to 10V J1 is closed and jumper J3 has pins 2 & 3 closed. The op-amp U3A operates as a 2X gain
amplifier. Q2 provides low impedance output drive.
0 to 20mA In this configuration jumper J1 is left open and jumper J3 has pins 1 & 2 closed. The op-amp U3A
operates as a unity gain amplifier. Op-amps U1A & U1B form a voltage to current converter.