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
max
/ Ω=U
Supply
/
V ∙ 25 (Ω/V) – 200 Ω
25 Ω ≤ R
max
Ω 200 Ω
(6-1)
R
max
in Ω
U
supply
in V
25
9
50
10
100
12
150
14
200
16
Tab. 1:
Determining the load resistance based on the supply voltage
4.3.4 Calibration
Output
quantity X
Output range Quantity equation
For-
mula
T in °C
-20°C...120°C
/
U / V
.
X
R / Ω 8750
- 55°C
(°C
°C =
/A)
(6-2)
RH in %
0%...100%
/
U / V
.
X
R / Ω
6250
- 25%
(%
% =
/A)
(6-3)
H20; H40
in %
0%...100%
/
U / V
.
X
R / Ω
6666,67
- 33,33%
(%
% =
/A)
(6-4)
AH in ppm 0ppm...AHScl
/
U / V
.
X
R / Ω
ppm =
AHScl / ppm
16
.
10
-3
A
-
AHScl / ppm
4
(6-5)
P; P40
1...5
=
U / V
.
X
R / Ω
266,67
- 0,3333
1
A
( )
< 5 mA: Teaching in or
sensor partially exposed to
air
(6-6)
C; C40 in
pS/m
100pS/m...
1000100 pS/m
=
U / V
.
X
R / Ω
6,667
- 333233
pS
A
( )
/
pS/
m
.
10
7
pS
m
< 5 mA: Teach-in
(6-7)
AP in %
0%...100%
=
U / V
.
X
R / Ω
6250
- 25 %
%
A
( )
(6-8)
L in %
0%...100%
=
U / V
.
X
R / Ω
6250
- 25 %
%
A
( )
(6-9)1
log(C);
log(C40) in
pS/m
1pS/
m...1000000
pS/m
=
U / V
.
X
R / Ω
375
pS
A
(
)
/
pS/m
-
10
1,5 log
(
)
pS
m
(
)
(6-10)2
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
12
20
T in °C
-20
-11.25
50
120
RH, H20,
H40 in %
0
6.25
50
100
AH in ppm 0
0.0625*AHScl 0.5*AHScl AHScl
P; P40
Teach-in
mode en-
abled
1
2.867
5
C; C40 ibn
pS/m
Teach-in
mode en-
abled
100
466807
1000100
log(C);
log(40) in
pS/m
1
2.37
1000
1000000
AP:
0
6.26
50
100
L
0
6.25
50
100
Tab. 3:
Scaling the analog current outputs
11
Bühler Technologies GmbH
BX150104 ◦ 03/2021
