QTech Data Systems DNP3 RTU - Manual (Page 19)

DATRAN XL4 RTU – Owners Manual – v1.1 June 2012
www.qtech.co.nz Page 19
Analog Analog Analog Analog Inputs Inputs Inputs Inputs
Single Ended or Differential Configuration Single Ended or Differential Configuration Single Ended or Differential Configuration Single Ended or Differential Configuration
Analog input channel pairs 1 & 2 and 3 & 4 can be individually configured to become differential inputs. In this
configuration channel 1 and 3 are the positive inputs, and channel 2 and 4 are the negative inputs.
Note. Differential analog inputs provide for non ground referenced negative inputs and provide up to 10 volts
common mode rejection on analog input signals.
Note. Differential inputs can be used as part of a multi-drop current loop arrangement.
Single Ended Input Details Single Ended Input Details Single Ended Input Details Single Ended Input Details
The diagram below shows the single ended analog input circuit. The circuit includes an analog preconditioning
network and unity gain buffer to produce a scaled 0 to 5 volts output to the Q04. The Q04 then converts that to a 0
to 2.5V value.
Circuit details of Single Ended Analog Input Channel.
The following paragraphs describe the various single ended Analog input configurations:
0 to 5V In this configuration jumper J5 has pins 2 & 3 closed and jumper J6 is left open. The analog input
voltage is fed via a 100k resistor to the non-inverting input of the op-amp. In this configuration the
input impedance is high and negligible current is drawn from the analog source.
0 to 10V In this configuration J5 has pins 1 & 2 closed and jumper J6 pins 2 & 3 closed. Resistors R1 and
R3 form a voltage divider that divides the analog input voltage by 2 to produce a 0 to 5 volts input
to the non-inverting input of the op-amp. In this configuration the input impedance is 20k and the
input current at 10V input is 500uA.
0 to 20mA In this configuration jumper J5 has pins 2 & 3 closed and jumper J6 pins 1 & 2 closed. The analog
input current flows through the 250 ohms resistor so that 0 to 20mA produces a voltage of 0 to 5
volts to the non-inverting input of the op-amp. In this configuration a voltage drop of 5 volts at
20mA is created in the 20mA loop by the Q22.
4 to 20mA The 4 to 20mA loop configuration is the same as the 0 to 20mA loop described above, except the
central processor scales the output to 4 to 20mA range. This reduces the ADC resolution to 80%
of the 1024 counts for full scale to 1 part in 800 counts.
Note. Each of the single ended analog inputs are clamped with BAV99 high speed switching diodes to both
ground and +15 volts to keep the input voltage to the op-amp in the range 0 to +15 volts. 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.
Differential Input Details Differential Input Details Differential Input Details Differential Input Details
Analog input channels 1 & 2 and/or 3 & 4 can be configured together to form two separate differential input
channels. When configured as differential inputs analog input channels 1 and/or 3 are the positive inputs and
analog input channels 2 and/or 4 are the negative inputs.
The diagram below shows the differential analog input circuit. The circuit includes an analog preconditioning
network and a unity gain differential op-amp to produce a scaled 0 to 5 volts output to the Q04 Processor.