Carel srl: pCO Stage Controller
page 29
APPENDIX A: TROUBLESHOOTING
The unit does not start (the mains presence LED on the main board is off, the LCD is off, the other LEDs are off).
Check:
a) the mains;
b) that after the 230V~ - 240V~ power transformer there are 24V~;
c) that the 24V~ power connector has been correctly plugged in;
d) the fuse of protection (
Fig. 18
on page 18);
e) the proper connection between the terminal unit (if present) and the main board.
At the start-up one of the following conditions occur:
alarm LED indicator ON;
no messages or random messages on the LCD;
buzzer ON.
Check:
a) EPROM polarity (see
Fig. 27
);
b) the pins of the EPROM (do not bend them when inserting the EPROM into its socket);
c) the microprocessor chip: if damaged, call the Maintenance Service.
Wrong input signal reading
Check:
a) the probe connection;
b) the distance of the cables carrying the probe signals from possible noise sources (e.g. power cables, contactors,
high voltage cables and cables with devices that are connected with high absorption at starting);
c) input calibration (by program);
d) the proper power supply to the main board and the probes;
e) the separation of the power supply of the digital inputs from the power supply of the pCO.
EEprom failure alarm
a) Contact the Maintenance Service
Uncertain alarm signal from digital input:
Check:
a) the input alarm signal - detect voltage between the "C" common terminal and the digital input terminal indicating
the "Cn" alarm. If voltage is present (24V~ or V
, according to the power supply being used for the digital
inputs) the contact of the connected alarm device is closed. If voltage is 0V~ or 0V
(see above) the contact is
open. If not differently stated, the controller gives alarm whenever the contacts are open.
Wrong reading of the input signals:
Check:
a) the probe connection (see page 24 and following);
b) the distance of the probe cables from possible electromagnetic noise sources (e.g. power cables, contactors,
high voltage cables and cables connected to high absorption at starting);
c) the presence of a high thermic resistence between the sensor and the probe socket. If required, add some paste
or conductive oil to the sockets;
d) in case of probe error or conversion error of the pCO, the verifications depend on the type of probe.
Active temperature/humidity probes with -1V-1V/
÷
1V1V signal: measure the probe signal between the terminals Bn
and AVSS with a voltmeter. The correspondence between voltage and value should be 10 mV
every °C/20% RH.
For example: when reading 230 mV
(0.2 V
) the probe sends out a signal corresponding to 20 °C/20% RH;
using the same logic, 0 mV
correspond to 0 °C/0% RH.
Pressure probes: in case of errors in the reading of these probes, check:
•
that analog inputs accept 4-20 mA signals (see
Fig. 23
on page 35).
•
the limits set via software correspond to the probes being used.
Measuring with a voltmeter the voltage at the terminals Bn and AVSS your indirectly obtain the current of the
probe signal, since the input impedance is 50 ohms (I=V/R).
The "Ps" (pressure) value can be obtained as follows (SB=Scale Bottom):
PS = (Vmeas./50 - 0,004) (SBmax. - SBmin.)/0.016 + SBmin.
Example: the probe used has a SBmin. = -0.5 Bar/SBmax. = 7 Bar; the read voltage equals Vmeas. = 0.5 V
.
The Ps pressure that the probe is measuring is:
Ps = (0.5/50 - 0.004) x (7 - (-0.5)) / 0.016 + (-0.5) = 2.3 Bar
•
Check that the capillary probe is not clogged.
NTC probes: the probe signal is an ohm value that depends on temperature.