Effect Of Zener Barriers On The Function Of The; Measurement Chain (Choice Of Excitation Voltage) - HBM SD01A Bedienungsanleitung

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3.3 Effect of Zener barriers on the function of the

measurement chain (choice of excitation voltage)

Series resistance in the supply lead is the main problem for measurement
accuracy. The voltage drop due to this line resistance must be corrected by
the excitation voltage output stage of the amplifier.
This is only possible up to the maximum output stage control voltage ("6 V
peak value, approx. 8.5 V
Zener barrier (from 6.5 V onward a noticeable effect can be expected).
The voltage drop on the cable must also be taken into consideration (loop
resistance 282 Ohm/km).
Example:
D Excitation voltage 1 V
D Transducer 6 x 350 Ohm = 58.2 Ohm
D Zener barrier resistance max. 2 x 106 Ohm = 212 Ohm
D Voltage at the amplifier without cable = 0.7 / 58.2 * (212+58.2) = 3.25 Vs
D Voltage at the amplifier with 500 meters cable = 0.7 / 58.2 *
(212+141+58.2) = 4.95 V
This calculation results in the following limits for maximum possible cable
lengths:
Transducer
max. 6 x 350 Ohm
max. 2 x 350 Ohm
3 x 350 Ohm
4 x 350 Ohm
max. 3 x 350 Ohm
4 x 350 Ohm
5 x 350 Ohm
6 x 350 Ohm
1 x 350 Ohm
1 x 350 Ohm
2 x 350 Ohm
If the required cable length cannot be implemented with a certain excitation
voltage it should be reduced.
CAUTION
The maximum cable lengths resulting from a consideration of the
safety engineering aspects must be checked separately!
HBM
) and is limited by the voltage limiter on the
rms)
= " 0.7 Vs
rms
Excitation
1 V CF or DC
2.5 V CF
2.5 V CF
2.5 V CF
2.5 V DC
2.5 V DC
2.5 V DC
2.5 V DC
5 V CF
5 V DC
5 V DC
Max. cable length
500 m
500 m
250 m
50 m
500 m
300 m
150 m
25 m
100 m
500 m
100 m
SD01A
A1045−2.4 en/de/fr