75
To adjust an alarm setpoint select 'SPx1' or
'SPx2' and press
P
which will reveal the current
setting. Each digit of the setpoint may be
adjusted using the
Up
and
Down
push-buttons,
and the
P
button to move control to the next digit.
When the required setpoint has been entered,
pressing
E
will return the display to the 'SPx1' or
'SPx2' prompt from which the other setpoint may
be selected, or the instrument may be returned to
the display mode by pressing
E
again.
Note:
Direct access to the alarm and control
output setpoints is only available when the menu
is enabled - see section 4.6.10
4.7 OPTIONAL 4/20mA OUTPUT
The BA364D can be supplied with an optional
4/20mA output which may be programmed to
produce an analogue output proportional to the
whole or part of the speed display. See section
1.9.7.1 for intrinsic safety details.
4.7.1 Programming and adjustment
The main tachometer programme menu is
extended as shown in Fig 4.6 to accommodate
the 4/20mA calibration functions.
The ‘4-20 OP’ programme function allows the
4/20mA output current to correspond to any
speed display. e.g. 4mA could represent 0rpm
and 20mA 500rpm.
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
‘Function’ 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 BA364D displaying ‘4.000’, this is the prompt
for setting the speed 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
speed 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 required speed has been entered,
press the
E
button to return to the ‘4.000’ prompt.
To enter the speed display at which the output
current will be 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 speed display increases, and
most instruments will produce a linear output
between 3.5 and 22mA.
Fig 4.6 4/20mA output programme structure
Note:
If the speed display calibration is changed
by adjusting the rotational scale factor r SCALE,
the timebase t-bASE, or the position of the
displayed decimal point, the 4/20mA output will
automatically be set to give a constant 3.5mA
output irrespective of the speed display. The
4/20mA output must therefore always be
recalibrated following recalibration of the speed
display.
