ZES ZIMMER LMG450, User Manual

Page: 243 / 306

Z E S ZIMMER Electronic Systems GmbH Chapter 12
243
When using the AC+DC coupling instead of the AC coupling, you get different errors. In this
case you might get an additional DC current of
∆
I
DC
=
±
(10
µ
V/Ri)=
±
(10
µ
V/2m
Ω
)=
±
5mA.
This error influences the TRMS value in the following way:
I I I
trms ac dc
= + 2 2
∆ ∆ ∆
I
I
I
I
I
I
I
trms
trms
ac
ac
trms
dc
dc
= ± +






∂
∂
∂
∂
* *
∆ ∆ ∆
I
I
I
I
I
I
I
trms
ac
trms
ac
dc
trms
dc
= ± +






* *
With an reading of I
dc
=0.00112A you get:
mA mA
A
mA
mA
A
A
I
trms
3559 . 2 5 *
95 . 0
12 . 1
35 . 2 *
95 . 0
95 . 0
± =






+ ± = ∆
For the active power you have an additional error of
±
(10
µ
V²/Ri/V
DC
)=
±
(10
µ
V²/2m
Ω
/V
DC
)=
±
5mW/V
dc
. So with a reading of U
DC
=0.013V you get a total error of
W mV
V
mW
W U
V
mW
P P
DC tot
638065 . 0 13 * 5 638 . 0 * 5
± =






+ ± =






+ ∆ ± = ∆
For the apparent power you get:
∆ ∆ ∆
S
S
U
U
S
I
I
= ± +




∂
∂
∂
∂
* *
VA mA V V A I U U I S 83975 . 0 ) 35 . 2 * 230 315 . 0 * 95 . 0 ( ) * * (
± = + ± = ∆ + ∆ ± = ∆
Please note that in this case you have to use
∆
I
trms
for
∆
I!
If you use external sensors please see the ZES Sensors and Accessories Manual for hints, how
to calculate the total uncertainty under this circumstances.
12.1.2 Accuracy of non sinusoidal signals
The standard accuracies are just given for sinusoidal signals. The reason is, that the national
standards usually work just with sinusoidal signals.
To estimate the error of non sinusoidal signals you can use the following system.
Let’s assume you want to measure a square signal with 5V peak value, 50% duty cycle, no DC
value and a frequency of 100Hz.