Instructions for Use
– SCHMIDT
®
Flow Sensor SS 20.600
Page 23
Wiring of impulse output 1
(PNP)
The impulse output is current-limited, short-circuit protected and has the
following technical characteristics:
Design:
Highside driver, open collector (PNP)
Minimum high level U
S,H,min
:
U
B
– 3 V (with maximum switching current)
Maximum low level U
S,L,max
:
0 V
Short circuit current limitation:
Approx. 100 mA
Maximum leakage current I
Off,max
: 10 µA
Minimum load resistance R
L,min
:
Depending on supply voltage U
B
(see below)
Maximum load capacitance C
L
:
10 nF
Maximum cable length:
100 m
Wiring:
Figure 4-3
The impulse output can be used as follows:
Direct driving of low-impedance loads (e.g. optocoupler, relays, etc.)
with a maximum current consumption of approx. I
L,max
= 100 mA.
This allows calculating the minimum permitted (static) load resistance
R
L,min
depending on the operating voltage U
B
16
:
𝑅
𝐿,𝑚𝑖𝑛
=
𝑈
𝐵
− 3 𝑉
𝐼
𝐿,𝑚𝑎𝑥
=
𝑈
𝐵
− 3 𝑉
0.1 𝐴
Example:
In case of the maximum operating voltage of U
B,max
= 28.8 V the minimal
load is R
L,min
= 258
Ω.
Here the excessive heating power of the load has to be considered.
The pulse output is protected by means of different mechanisms:
Current limiting:
The current is limited to approx. 100 mA (analog).
If the resistance values are too low, the length of the interconnection
phases is limited to 100 µs.
The maximum load capacitance C
L
is 10 nF. A higher capacitance re-
duces the limit of the current limiter.
16
Overcurrent peaks are absorbed by the short circuit limiter.
