Carel MPXPRO User Manual page 45

Important : if the double thermostat function is activated, the
setting of the following parameters has no eff ect:
• r6 (probe for night-time control);
• r4 (automatic night-time set point variation).
Control off set with probe error (parameter ro)
Par. Description
ro Control off set with probe error
MPXPRO in standard mode uses the virtual probe Sv for control, that is,
the weighted average of the outlet and intake probe (see parameter /4).
If one of the two probes making up the virtual probe is broken or has
an error, parameter ro is used to continue normal control in controlled
conditions, without the need for immediate intervention by maintenance
personnel. The recommended value of ro is the temperature diff erence
between the outlet probe and intake probe reading in steady operating
conditions of the refrigeration unit:
ro = Sr – Sm
If ro=0 the function is not active. The following cases may occur:
• outlet probe Sm error: MPXPRO starts control based on the intake
probe Sr alone, considering a new set point (St*) determined by the
formula:
St* = St + ro
• intake probe Sr error: MPXPRO starts control based on the outlet probe
Sm alone, considering a new set point (St*) determined by the formula:
St* = St - ro
If night-time operation has been set with the intake probe as the control
probe, the controller considers /4=100 and uses the outlet probe. The
new set point becomes:
St* = St – ro
Note:
• if ro=0 the function is not active;
• for night-time operation the new set point is added to the value
defi ned by r4 (= automatic night-time set point variation);
• in the event of errors on both probes, the controller switches to duty
setting operation, see paragraph 6.6.
Example: Sm fault in daytime operation, with /4=50, St=-4, Sr=0, Sm=-8,
ro (recommended) = 0-(-8) =8. The new control probe will be Sr with:
St* = St + ro
Therefore St*= -4+8 ·(100-50)/100=0
If the fault is on Sr, the new control probe will be Sm with:
St* = St - ro
Therefore St*= -4-8 ·50/100=-8.
Def Min Max UoM
0.0 0.0 20 °C/°F
Tab. 6.e.d
(100 – /4)
100
/4
100
(100 – /4)
100
/4
100
Maximum and minimum temperature monitoring
(parameters r5,rt,rH,rL)
For the procedure to enable monitoring, see paragraph 3.7.
Par. Description
rt Duration of current maximum and
minimum temp. monitoring session.
rH Maximum temp. acquired in the session
rL Minimum temp. acquired in the session
r5 Maximum and minimum temperature
monitoring probe
0 = monitoring disabled
1 = control probe (Sreg)
2 = virtual probe (Sv)
3 = outlet probe (Sm)
4 = defrost probe (Sd)
5 = intake probe (Sr)
6 = superheated gas temp. probe (tGS)
7 = saturated evaporation temperature
probe (tEu)
8 = auxiliary defrost probe (Sd2)
9 = auxiliary probe (Saux)
10 = auxiliary probe 2 (Saux2)
ON time for duty setting operation(parameter c4)
Duty setting is a special function used to maintain control in emergency
situations with errors in the temperature control probes, until the service
intervention. In the event of a temperature probe error, MPXPRO uses the
other probe available and adjusts the set point according to the setting
of parameter ro. In the event of errors on both probes, MPXPRO switches
to Duty setting mode. The controller is activated at regular intervals,
operating for a time equal to the value set for the duty setting parameter
c4, and off for a fi xed time of 15 minutes.
Par. Description
c4 ON time for duty setting operation (Toff =
15 minutes fi xed)
0 = compressor/valve always OFF;
100 = compressor/valve always ON
R
ON
OFF
Key:
R Control
c4 ON time
With Duty setting active, during the ON time the compressor icon
remains on, while it fl ashes during the OFF time.
Important : during duty setting, the compressor protection times
are not observed.
The table below describes the possible fault situations relating to the
control probes and the function that is activated.
Type of system Control probe fault
Sm

1 probe

2 probes

* ro must be >0.
45
Def Min Max
- 0 999
- - -
- - -
0 0 10
Def Min Max
0 0 100
t
c4 15 min
Fig. 6.j
t Time
Control Parameter
Sr
Duty setting

Duty setting
control on Sr

control on Sm

Duty setting
MPXPRO - + 0300055EN rel. 1.1 30/08/10
ENG
UoM
hour
°C/°F
°C/°F
-
Tab. 6.e.e
UoM
min
Tab. 6.f.b
c4
c4
ro(*)
ro(*)
c4
Tab. 6.f.c