19
Advantages:
- The Voltage stabiliser, inside the cell, keep insensible the excitation of the cell
to the voltage drops due to the length and to temperature changes of the
connection-cable.
With power voltages around 15 Vdc, distances cell/electronics of several
kilometres are acceptable!
- The internal amplifier and the high voltage output (± 5 V) bring the signal
insensible to the external noise (great Signal/Noise ratio).
Disadvantages:
none.
8.2.2 Current amplifier (see paragraph 8.6 and further diagram): (2 - wires)
- A 4 = supply voltage (= V
ps)
: from 15 to 40 Vdc; Signal output: 4-20 mA;
(Typical power supply is 24Vdc filt. Stab. with an external RL=250 Ohm load
resistance)
Advantages:
- As for the voltage amplifiers (-A5; -A1).
- Saving (insignificant) of a lead in the connecting cable.
-
Immunity to electrical noise on the cable and to drop of voltage due to cable
resistance.
Disadvantages:
- Low output signal from the strain-gauge bridge, very high amplifier gain and,
consequently, high sensitivity to the electrical disturbances of the signal before
amplification reduce the potential resolution.
In fact: excitation of the bridge (at zero load) =V=RI = 350 · 3 · 10
-3
= 1,05 V;
when, R= bridge resistance = 350 Ohm; I= 3mA (see Note below)
From which: bridge output signal = 2 · 1,05 = 2,1mV FS
against 2 · 10 = 20 mV/FS of the -A1 amplifier) (about 10 times less).
- Limitation on the choice of the further electronics.
Note: the total circuit at zero load is 4mA of which about 3 mA for the
bridge and about 1 mA for the internal current amplifier.
Содержание 500QD Series
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