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BCM-MS, BCM-LS
4.3.2 Analog Current Outputs (4..20 mA) - Measurement
With Load Resistor
To measure the currents of the analog current outputs, a load
resistor must be connected to each output as shown below.
Depending on the supply voltage, the load resistance should
be between 25 Ohm and 200 Ohm. A voltmeter can now be
used to measure the voltage which drops over the respective
resistance.
Sensor cover top view
Fig. 6: Connecting the load resistances to measure the analog
4..20 mA outputs
The default configuration is intended for oil temperature on
channel 1 and relative humidity on channel 2.
The channel assignment can be changed and is described in
chapter Setting Analog Current Outputs.
4.3.3 Load Resistor Size
The load resistance cannot be selected arbitrarily. It must be
adjusted to the supply voltage of the sensor. The maximum
load resistance can be calculated using the formula (6 -1). Or
you can alternatively use the table here.
R
/ Ω=U
/
25 Ω ≤ R
max
Supply
V ∙ 25 (Ω/V) – 200 Ω
R
in Ω
max
25
50
100
150
200
Tab. 1: Determining the load resistance based on the supply voltage
BX150104 ◦ 03/2021
Ω 200 Ω
(6-1)
max
U
in V
supply
9
10
12
14
16
4.3.4 Calibration
Output
Output range Quantity equation
quantity X
T in °C
-20°C...120°C
RH in %
0%...100%
H20; H40
0%...100%
in %
AH in ppm 0ppm...AHScl
P; P40
1...5
C; C40 in
100pS/m...
pS/m
1000100 pS/m
AP in %
0%...100%
L in %
0%...100%
log(C);
1pS/
log(C40) in
m...1000000
pS/m
pS/m
Tab. 2: Calculating the output parameter for the analog current out-
puts
By default, the current outputs show the temperature
between -20 °C and 120 °C and the relative humidity between
0 and 100 %. The upper limit for the absolute humidity (AHScl)
is required to scale the analog current outputs. This is freely
programmable. However, the limit is oil-specific and must be
determined at a laboratory along with the other parameters
required to measure the absolute humidity.
Please contact Bühler Technologies GmbH Service in this re-
gard. The current outputs are scaled linear.
lout in mA 4
5
T in °C
-20
-11.25
RH, H20,
0
6.25
H40 in %
AH in ppm 0
0.0625*AHScl 0.5*AHScl AHScl
P; P40
Teach-in
1
mode en-
abled
Teach-in
C; C40 ibn
mode en-
100
pS/m
abled
log(C);
1
2.37
log(40) in
pS/m
AP:
0
6.26
L
0
6.25
Tab. 3: Scaling the analog current outputs
U / V
.
/
°C =
(°C
/A)
- 55°C
X
R / Ω 8750
U / V
.
/
6250
(%
/A)
- 25%
X
% =
R / Ω
U / V
.
/
6666,67
(%
/A)
- 33,33%
X
% =
R / Ω
U / V
AHScl / ppm
AHScl / ppm
.
X
/
ppm =
-
.
-3
A
4
R / Ω
16
10
U / V
1
( )
.
- 0,3333
X
=
266,67
A
R / Ω
< 5 mA: Teaching in or
sensor partially exposed to
air
pS
pS
U / V
( )
pS/
.
.
- 333233
X
/
m
7
=
6,667
10
A
m
R / Ω
< 5 mA: Teach-in
%
U / V
( )
.
- 25 %
X
=
6250
A
R / Ω
%
U / V
( )
.
- 25 %
X
=
6250
A
R / Ω
pS
U / V
.
pS
(
-
)
(
)
(
1,5 log
375
pS/
m
10
A
X
/
m
=
R / Ω
12
20
50
120
50
100
2.867
5
466807
1000100
1000
1000000
50
100
50
100
Bühler Technologies GmbH
For-
mula
(6-2)
(6-3)
(6-4)
(6-5)
(6-6)
(6-7)
(6-8)
(6-9)1
)
(6-10)2
11
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