24
The pulse output will sink up to 10mA. When
closed the voltage between the pulse output
terminals P1 & P2 will be less than 3V when
switching 5mA.
Fig 14 Typical application of pulse output
8.6 4/20mA output
The optional 4/20mA output may be programmed
to produce an analogue output proportional to the
whole or part of the rate display. The output is a
current sink which requires between 5 and 30V to
function as shown in Fig 15.
Fig 15 Application of 4/20mA output
8.6.1
Programming and adjustment
The main programme menu is extended as shown
in Fig 16 to accommodate the 4/20mA calibration
functions.
The ‘4-20 OP’ programme function allows the
4/20mA output current to correspond to any rate
display. e.g. 4mA could represent 10
litres/minute and 20mA 100 litres/minute.
To calibrate the 4/20mA output current, enter the
programme mode by operating the
P
and
E
push-
buttons simultaneously. If the instrument is not
protected by a security code the first parameter
‘UPdAtE’ will be displayed. Enter the security
code if the instrument is protected.
Using the
Up
or
Down
push button select the
function ‘4-20 OP’ and press
P
which will result in
the BA538C displaying ‘4.000’ which is the prompt
for setting the rate display corresponding to an
output current of 4.000mA. Pressing
P
will reveal
the existing setting with the most significant digit
flashing. The decimal point will be fixed in the
position already defined for the rate display by the
‘d.P’ function. The value of the flashing digit may
be changed by pressing the
Up
or
Down
buttons.
When this digit is set as required, pressing
P
will
transfer control to the next digit.
When the flow rate corresponding to an output
current of 4mA has been entered, press the
E
button to return to the ‘4.000’ prompt.
To enter the rate display corresponding to an
output current of 20.000mA, press the
Up
or
Down
button to select the ’20.000’ prompt followed by
P
to
reveal the current setting. This may be
changed in the same way as the 4mA setting.
When set as required, press
E
three times to
return to the display mode via the ‘20.000’ and ‘4-
20 OP’ prompts.
The 4/20mA output may be calibrated to increase
or decrease as the rate display increases, and
most instruments will produce a linear output
between 3.5 and 22mA.
Note 1:
If the rate display calibration is changed
by adjusting the rate scale factor SCALE-r, the
timebase t-bASE, or the position of the rate
display decimal point, the 4/20mA output will
automatically be set to give a constant 3.5mA
output irrespective of the rate display. The
4/20mA output must therefore always be
recalibrated following recalibration of the rate
display.
Summary of Contents for BA538C
Page 8: ...8 ...
