Bacharach GDA-1600, Instructions Manual

Page: 15 / 54

Instruction 5700-9001 GDA-1600 16-Channel Controller
15
Entries Description
Sensor Direct
with Local Cal
Sensor Direct is identical to Analog with Local Cal and both activate the GDA-1600’s
Cal Mode
features (see section 3.2.7 on page 19). Problems may arise if calibrations
are performed in two places upon the same signal so that Cal Mode menus become
visible only when Sensor Direct or Analog with Local Cal is selected. These
selections should only be used when the input originates from a non-calibrated
signal source such as the
Bridge Sensor Input
option described in section 4.2.3 (page
31), or, our GDX-150 Transmitter with a non-calibrated 4-20mA output. These
applications require the GDA-1600 to be used as the calibration point since the
sensors have no
zero
or
span
controls.
12-bit analog inputs may be direct from Sensor Input options of Voltage/Current
Input options.
Analog Input
with Local Cal
Analog with Local Cal is available when the GDA-1600 will be the point of calibration
for the analog input.
Analog Input
Analog Input
should be selected when the channel’s input comes from a transmitter
or monitoring device with a calibrated output such as 4-20mA.
Modbus 16 Bit The Modbus 16 Bit menu may be used with most wireless modems if a wireless
Modbus interface is required. Modbus 16 Bit is returned as an integer that can be 0
to 65536. Typically, a slave will put out a number with say 10bit (0-1023) or 12bit (0-
4095) resolution to represent a range value. In the GDX-350, this value is 12 bit and
is ranged in a 4-20 mA style signal where 4mA sends a value or counts of 800 (min
raw) and 20mA sends a value or counts of 4000 (max raw). A slave with a 10-bit
output would send 200 for 4mA and 1000 for 20mA.
The Modbus Master RS-485 port supports most integer types, resolutions, and
formats. “MODBUS 16 BIT” menu indicates that 16-bit is the maximum
MB 16 Bit
Signed
, but also
supports 8-, 10-, and 12-bit formats by editing the Min/Max Raw menus to contain
the correct counts ranges.
Modbus 16 Bit Signed sends 15 data bits and the MSB indicates the sign bit. If the
bit is set, the value is negative and positive if not set. In this case, the min raw is
usually zero and the max raw is set to the full scale value.
Wireless RF900 The
Wireless RF900
input option should only be used with our proprietary wireless
monitors.
Modbus 32 Bit
Modbus 32 Bit represents a IEEE754 data format that requires no scaling between
min raw and max raw values. The value is read directly by the firmware and is
displayed in the format sent by the slave.
NOTE: Most slaves do not implement a means to determine if the value is valid or
faulty. Generally, they return a zero value with a fault present (requiring additional
data registers be read to determine the validity of the data). There is no standard
defining how this is done, so this option typically requires special firmware drivers.
(Compare this to 16-bit data types, in which the value is driven negative below the
controller’s fault level which generates a fault alarm trip. This, along with expected
cal data values can be achieved by reading a single register.)