CSE Kingfisher PLUS+, Hardware Reference Manual

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Superseded Hardware Manual 7.12 Page 68
1.23 RT-1: An a lo g RTD In p u t, 4 Ch a n n e l
The RT-1 RTD input module provides four input channels for Pt100 Resistance Temperature Devices,
each capable of converting the 100
Ω
(DIN standard) temperature sensor to a digital signal for use as
required by your application. Modules are available in the standard range of -150 to 400°C or can be
manufactured to special order with minimum 100°C span in the -150 to 400°C range.
Conversion speed for each of the four channels is 20
µ
S and this provides a maximum update rate of
two milliseconds for the module. Resolution of the converted signal is 12 bits binary (1 part in 4096)
over the range. The placement of the 12 bits from the A/D converter in the #AI data word is shown
below. The relationship between the temperature and the data from the A/D converter is shown in the
figure below.
MSB
LSB
0 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 0 0 0
The input circuit features a constant current RTD excitation using the third lead of the RTD to sense
and compensate for the RTD lead resistance, resulting in an accurate RTD temperature
measurement. The RTD voltage is then amplified and fed to the 12-bit ADC. The module is factory
calibrated to provide 0.1% resolution of span.
To ensure accurate operation each input is factory calibrated using Toolbox 32 software. The
calibration is stored in EPROM on the RT-1 and is therefore non-volatile.
32760
0 400
DegC
Raw Value
-150
-150 t
o 400 D
egC
Figure: RT-1 Scaling
Input protection for the module is sufficient to guarantee operation with reduced performance with up
to 1500 V common-mode. The module provides electrical isolation of externally generated noise
between field wiring and the backplane through the use of optical isolation.
To minimise the capacitive loading and noise, all field connections to the module should be wired
using a good grade of twisted, shielded instrumentation cable. The shields can be connected to E. The
E connection provides access to the backplane (frame ground).
Four red LEDs labelled A1 to A4 on the faceplate are ON when an RTD is connected. A green LED at
the top of the faceplate is ON when the module is operating correctly. This module also consumes
power from the +5 VDC and 12 VDC bus. A 24 VDC isolated converter is used to provide power to the
RTD conditioning and ADC circuits. This module can be installed in any I/O slot of a 4, 6 or 12 slot
backplane in a system. Up to 10 RTD modules can be installed in a backplane.