VEGA VEGADIF 34 … 51 - Manual (Page 36)

36 VEGADIF 34 … 51
20094-EN-030731
Adjust span without display
1) Set pressure for span precisely (e.g.
1 bar) and check via an external pressure
calibrator.
2) Push the s+ and s– keys simultaneously.
The pressure (e.g. 1 bar) corresponds to the
output current 20 mA.
Adjust zero/span without display, however
with current ammeter
For adjustment, a control instrument with
measuring range 0 … 20 mA is connected to
terminal 1 and tag 1.
1) Set pressure for zero precisely (e.g.
0 bar) and check via an external pressure
calibrator.
2) Adjust with the z+ and z– keys a current
of 4 mA.
The pressure (e.g. 0 bar) corresponds to the
output current 4 mA.
3) Set pressure for span precisely (e.g.
1 bar) and check via an external pressure
calibrator.
4) Adjust with the s+ and s– keys a current
of 20 mA.
The pressure (e.g. 1 bar) corresponds to the
output current 20 mA.
Note:
If only intermediate values are available for the
reference pressures, the current to be ad-
justed can be also calculated:
p – p
z
I = 4 mA + 16 mA • –––––––––
p
s
– p
z
p = Reference pressure
p
s
= Pressure at span
p
z
= Pressure at zero
Set-up
Example:
Meas. range 0 … 1000 mbar
Reference pressures span p
s
= 1000 mbar,
zero p
z
= 0 mbar, reference pressure
p = 250 mA (750 mbar)
250 mbar – 0 mbar
I
z
= 4 mA + 16 mA • ––––––––––––––––––––
1000 mbar – 0 mbar
I
z
= 8 mA
750 mbar – 0 mbar
I
s
= 4 mA + 16 mA • –––––––––––––––––––
1000 mbar – 0 mbar
I
s
= 16 mA
Position adjustment display (bias
pressure)
In some cases the display does not show
zero for zero pressure when setting zero.
These can be the reasons:
- effective pressure lines have different fillings
- asymmetrical routing of the capillary cables
- position-dependent measuring cell (max.
2 mbar by 90° tilt).
The function „Save/accept bias pressure“
saves the available pressure as correction
value and sets the display to zero. The pres-
sure values for zero and span are now shifted
by the bias pressure (see example below).
This shift is only possible up to the editing
limits. This shift does not affect the current
output.
Example:
Save/accept before bias pressure
Zero 0.000 bar, span 0.500 bar
Display = -0.002 bar
Save/accept after bias pressure
Zero 0.002 bar, span 502 bar
Display = 0.000 mbar.