Dewetron DAQP-MULTI, Technical Reference Manual, Page: 11 / 18

11
DAQP-MULTI / DAQP-THERM
Block diagram
The base block diagram of the DAQP-MULTI and the DAQP-THERM gives an idea of the internal structure.
EXC+
IN+
EXC-
EXC-
9-pin DSUB
INPUT
CONNECTORS
9-pin DSUB
OUTPUT
CONNECTOR
RTD & Voltage input (DAQP-MULTI)
100M
TC+
TC-
INPUT
CONNECTORS
Thermocouple input (DAQP-THERM)
µV Amplifier
gain 64
Differential
amplifier
CJC sensor
with 0.01°
resolution
ADC
24 bit
125 kS/s
D
igital
S
ignal
P
rocessor
DAC
16 bit
250 kS/s
Input
protection
Sensor fault detection
Antialiasing
filter
IN-
DAQN-RTD
compatibility
jumper
GNDi-
TEDS-
GNDi
Input
protection
15 V compliance
voltage
programmable
constant current
x 1
x 50
1
2
7
8
6
4
9
1
Micro
controller
Vout
GND
RS485 A
RS485 B
+9 V
DC
DC
GNDi
-9 V
4
2
3
5
9
1000 V RMS
isolation barrier
Amplifier description
The DAQP-MULTI consists of two separate input amplifiers. The first one is optimized for thermocouple
measurement. Its main properties are extremely low offset drift and noise. The sensor is connected to a mini
thermocouple connector with copper contacts. A precision temperature sensor with a resolution of 0.01 °C
measures the temperature directly on the junction between the copper contact and the TC material of the
sensor connector. This minimizes the error due to the CJC and allows the connection of all TC types.
The second input combines a programmable constant current source and a differential input amplifier on a
standard DSUB9 connector. It allows all kind of resistance measurement as well as voltage measurement.
Bridge sensors using current excitation are also supported. The small input offset drift could be eliminated by
using the internal short circuit function.
The conditioned analog signal passes a low pass filter and then comes to an aliasing free analog to digital
converter. The digital data stream is isolated before getting into a high speed D igital S ignal P rocessor. It
allows the complete linearization and filtering with a very low signal delay. Linearization tables are stored
with up to 512 points which minimizes the nonlinearity error for thermocouples and RTD to less than 0.01°C.
The complete data processing internally runs at 125 kS/sec. The output digital to analog converter runs at
the double speed, 250 kS/sec. That improves the signal quality on the analog output. The measured value
is also available on the RS485 as an ASCII value. That allows using the module also as a full measurement
instrument without AD-Card or analog wiring.
450134 • DAQP/H SI /PAD Modules • Technical Reference Manual • Prin t ing version 2.3.4 • November 18, 2020