ECD electronics
A ß-radiator in the ECD ionizates the carrier gas.
The pulsed operating voltage forces a current. This
current decreases when components appear and
catch electrons.
This current is supplied by the detector electronics as
rectangle pulse with constant amplitude, 1µs pulse
width and 0,3 ... 300 kHz
The pulses are integrated and compared with the adju-
stable reference current (0 ... 400% => 0 ... 4x10
-9
A).
The amplifier adjustes the pulse frequency so that
measuring current equals reference current.
If the sample in the measuring chamber catches elec-
trons the measuring current decreases. Thus the pulse
frequency increases till measuring current and reference
current are equal again.
Reference current
The reference current of 100% = 1nA is optimum for
carrier gas nitrogen with a flow of 30 ml/min.
Range
Die Dynamik des ECD ist 2x10
4
. Weil der Detektorver-
stärker in einem Range eine größere Dynamik hat, gibt
es für den ECD keine Range-Einstellung.
Zero adjustment
The microcontroller on the detector module adjusts the
zero using software functions if an autozero is triggered
manually or by a time program.
Connection of detector
Refer to the connection diagram below.
0 ... 300 kHz, 1µs pulse width
Signal [kHz]
GND
Operating voltage +27 V
U
f
D
A
dt
Reference current
1nA
≈
100%
GND
Mm
GND
Mm
Measuring
current
X8
RUN
1
1
2
3
4
5
6
7
8
9
10
ECD am
lifier
X8
X3
Koax
ECD
green: operating voltage +27 V
blue: ground
X8
X201
X202
Detector A
X 202
X 201
Detector B
X 202
X 201
Detector electronics
8
9DETEKT.CHP, Stand Dezember 22, 1999
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