Yokogawa Data Acquisition with PID Control CX2000 - Manual (Page 8)

1-2 IM 04L31A01-01E
1.2 Input Section
A/D Assembly
The A/D assembly has items such as a programmable gain amp, voltage reference,
PWM modulator, current source for RTD measurements, differential amp, voltage source
for RJC, serial parallel converter, control logic, and an occurred scanner SSR control
signal.
The A/D assembly uses a sinewave oscillating type self-resonant switching power supply
(DC/DC converter), and noise filtering is achieved by signal integration.
The A/D assembly detects the frequency of the power while it is ON and the integrated
time becomes 20 ms or 16.67 ms. Therefore it carries a very high rate of noise rejection
for the power frequency (in auto mode).
In case the power frequency of the instrument and of the measured object are different,
the appropriate integrated time is manually selectable. In case of the CX2000, the
selection of 100 ms for 50/60 Hz is also available. A 16 bit resolution is achieved
regardless of the integrated time.
Input Terminal
The internal printboard is isothermal because a print board with a metal core is being
used. Therefore, stable reference junction compensation is realized.
Scanner Assembly
An in-house SSR (solid state relay) is being used for the scanner. The SSR, having a
semiconductor switch, has a withstand voltage as high as 1500 V and a leakage current
of only 1 nA. For that reason, it has the following features.
• Semi-infinite life due to the absence of mechanical contacts
• Silent operation
• No occurrence of thermoelectric power.
On the other hand, compared to a mechanical relay, the SSR has, the disadvantage of a
bigger ON resistance and OFF capacity. As a result, RTD measurement and noise
resistance characteristics are affected. Regarding RTD measurements, a differential
amp was inserted into the previously mentioned analog circuit without increasing the
number of parts, so that it would receive no influence from ON resistance.
For RTD measurements in Measurement input section there is generally no insulation
between channels.
For RTD measurements in Control input section there is generally insulation between
channels.
Data Storage Functions
For storing data, the CX1000/CX2000 has 1.2 MB of internal memory and is equipped
with a Zip drive, or an ATA flash memory card drive. The measured data can also be
saved to external storage media such as floppy disks, Zip disks, and ATA flash memory
cards.
Display Unit
The CX has a 5.5-inch (CX1000) or 10.4-inch (CX2000) TFT color LCD on which it
displays the measured results (240 (vertical)
×
320 (horizontal) pixels for the CX1000 or
480 (vertical) × 640 (horizontal) pixels for the CX2000).