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4.1.1.1
No Sensor
A common source of a trouble condition is an input channel that is configured for a sensor that does not exist. In this case, the system
expects to see current flowing within the current loop, but there cannot be current if there is no sensor connected. Either fix the miss-
wired sensor, or change the sensor type to NONE, section 3.3.3.2. After returning to normal mode (using the MENU key), the power
light should return to steady green. Be sure that the 4-20mA output on each sensor is set to “On”.
4.1.1.2
Wrong Sensor Type
If all channels are configured properly, another source a trouble condition could be the type of sensor attached to an input channel.
Macurco™ Toxic sensors can indicate high gas concentrations with signals of up to 24 mA in the current loop. However, a combustible
sensor can indicate a trouble condition with a 21 mA signal. Therefore, a toxic sensor connected to channel which is configured for a
combustible sensor can cause a fault indication if the gas concentration is high enough.
4.1.1.3
Sensor Trouble
All Macurco™ Sensors are either supplied with a STATUS lamp that will indicate the health of the device, or will display a trouble
condition on the digital display. Macurco sensors may be tested by depressing the TEST button on the sensor printed circuit board, or
(depending on the type of sensor), the button on the interior front panel of the unit. Macurco sensors will step the output current level
from 4 mA to 20 mA over the course of the warm-up period, allowing the technician to determine where the trouble condition exists. If
the sensor is still in a trouble condition, resetting the power may clear the trouble condition. Remove one of the power wires from the
sensor terminal strip causing the sensor to go through a power-up reboot. Be sure that the 4-20mA output on each sensor is set to
“On”.
4.1.1.4
Faulty Wiring
Finally, the wiring between the DVP-120 and the sensor should be investigated. The power input to the sensor should be investigated
at the sensor
. Since Macurco sensors are rated for operation between 12 and 24 VDC or VAC, the voltage drop between the DVP-120
and the sensor should not be an issue if the wiring guidelines in Table 2-2 are followed. A multi-meter can be inserted to check the
current flow within the loop, or a continuity test can be performed on all four wires between the DVP-120 and the sensor. Ensure power
is removed from the DVP-120 prior to removing the input or output connectors from the DVP-120 controller board. Be sure that the 4-
20mA output on each sensor is set to “On”.
4.1.1.5
Resettable Fuse
Each sensor channel is provided with a PTC-resettable fuse internal to the DVP-120 to protect against over current situations. To reset
a sensor channel, power should be removed from the channel. This can be accomplished by removing power from the sensor –
causing the loop current to go to zero, or by completely removing power from the DVP-120.
4.1.2
Internal Controller Board Trouble
If the sensor status display and investigative efforts reveal no problems with the input channel current loops and channel configuration,
the most likely trouble condition is an internal problem detected by the DVP-120 controller. In this case, contact the Macurco Technical
Service for advice and help.
4.2
Timed ventilation problem
When using the timed ventilation mode, the system clock should be checked regularly (at least twice a year). The battery backed real
time clock in the DVP-120 does not adjust for daylight saving time so the spring and fall switch over points are good choices to check
the system clock.
! WARNING
High voltage terminals (120/240 VAC) are located within the DVP-120, presenting a hazard to service technicians. Only qualified technicians should
open the DVP-120 case and service the internal circuits. Ensure power is removed from the DVP-120 prior to servicing the unit.
4.3
No Power
The DVP-120 starts up as soon as power is applied to the microcontroller, and the DVP-120 is designed to have power
continuously
applied to the unit. An external indication of successful power application to the unit is the immediate operation of the Status Lamps
grouped around the LCD. If the operator does not see immediate response from the status lamps, power should be checked at AC~
If the correct voltage is noted at AC~, then the internal fuse of the DVP-120 should be investigated. The DVP-120 is protected from
over-current and transient situations by the fuse at F3. AFTER removing power from the DVP-120, F3 can be checked by removing the
