Apparatus for process analysis

In an apparatus for process analysis, a test substance is removed from the process stream by a probe and fed to an analysis instrument with a measured value display. Upstream of the analysis instrument, the test gas is conveyed through condensers. A monitoring unit is coupled to the analysis instruments and the processing chain without influencing the flow of data from the analysis instrument to the measured value display. The monitoring unit receives information about the entire apparatus via status sensors which are incorporated into the processing chain and into the analysis instrument. Depending on this information, the monitoring unit can intervene via solenoid valves, switches and motor potentiometers into the apparatus and alter its operation. The condition of the apparatus can also be displayed.

BACKGROUND OF THE INVENTION 
The invention relates to an apparatus for the continuous or 
quasi-continuous analysis of test substances, which presents a closed 
system in that all external intervention can be avoided, provided that it 
is not necessitated by failure indications. If indications of failure do 
not throw the measured values produced into doubt, the measured values can 
be considered to be reliable. Routine operations (calibration, condensate 
delivery from a test gas condenser, blow-through of an extraction probe 
and the like) are carried out automatically. The test substances can be 
present in a gaseous or liquid phase. 
Process analysis measuring devices consist of an extraction device, a 
processing chain and at least one analysis instrument, the individual 
parts being designed in different ways depending on the object set. For 
example, the extraction device and processing chain are generally very 
simple in design for monitoring environmental air whereas they are usually 
of quite a complex configuration for measuring emission. The functioning 
of the analysis instrument is normally dependent upon the correct 
functioning of the extraction device and the processing chain. In process 
analysis measuring devices it is important for the measured values to be 
readily available and reliable. Up until now, daily checks of operation 
have generally been carried out by skilled workers to achieve sufficient 
availability and reliability. The analysis instruments are calibrated 
regularly to maintain the accuracy of measurement. This method of 
preventive maintenance has the disadvantage, in addition to the associated 
high cost, that disturbances occurring between two checks of operation can 
remain unnoticed. This applies, in particular, to those disturbances which 
do not affect the measurement value (for example, insufficient permeation 
of test gas due to a blockage). 
In the past, it has been proposed that the availability of analysis 
measurements be increased while simultaneously reducing the operating 
costs by using process computers. In this arrangement, the conditions of 
status sensors should be transmitted to a measuring device and the 
measured value to a central computer which examines the plausibility of 
the measured value and checks the operation of the measuring device using 
the status indications. The computer should be able to intervene in the 
measuring device and, for example, effect calibration by remote control. 
This design is only suitable for extensive measuring networks due to the 
associated cost (computer software, remote control system). Moreover, in 
principle, both the computer and remote control system threaten the 
availability of the measured values. 
Due to this fact, this design has hitherto only been adopted in 
environmental protection measuring networks as far as we know. 
There are some analysis instruments which indicate deviations from the 
desired operating condition by means of status displays. There are also 
auxiliary devices which carry out calibration according to a fixed time 
program or are initiated from outside. In this case, the analysis 
instrument is charged with null gas or sensitivity gas. In certain 
conventional commercial instruments, the measured values determined are 
stored and the following measured values are corrected electronically on 
the basis of the stored calibration values. The disadvantage of this 
method is that the measured value is transposed into a correction circuit. 
If this is absent, the measured value is not available. Although a failure 
indication is produced in these automatic balancing devices when the 
calibration values have drifted from a certain range, undetectable 
operating conditions in which incorrect values are stored can exist. In 
another instrument, which is marketed in conjunction with IR analysis 
devices, the zero point and sensitivity are adjusted on the analysis 
instrument by means of motor potentiometers. Although the measured value 
is not hereby corrected, defective adjustments are not identified by 
failure indications. 
The apparatuses just described have the disadvantage that only parts of the 
measuring device are monitored (status displays on analysis instruments) 
or only parts of the routine operations are automated (automatic 
equalization devices), the availability of the latter being impaired in 
principle by transposition of the measured value and/or irregular 
calibrations not being identified externally during routine operations. 
SUMMARY OF THE INVENTION 
An object of the invention is to increase the availability of process 
analysis measuring devices and to reduce the maintenance costs. 
This object is achieved according to the invention in that a conventional 
type of measuring device is provided with a monitoring unit which receives 
information about the entire measuring device by means of status sensors 
and from the measured values and intervenes in the measuring device by 
means of solenoid valves, switches and motor potentiometers and emits 
messages about the condition of the measuring device to the exterior. The 
number of measured values prevent the availability of the measured values 
from being impaired by the monitoring unit. 
The measured values are passed via a passive component and are not changed 
directly but by means of motorised adjusting potentiometers on the 
analysis instruments. Suitable definitions of the outputs of the 
monitoring unit allow the measuring device to assume its generally 
measurable basic condition in the absence thereof and to emit a failure 
indication to the exterior. At any time, the measuring device can be 
operated quite simply by actuating a switch in the as yet conventional 
manner and without the possibility of intervening in the monitoring unit. 
The measuring device is monitored by checking the condition of the status 
sensors and by continuously examining the plausibility of the measured 
value. If a disturbance occurs, failure indications are emitted to the 
exterior and, if possible, an intervention is made into the measuring 
device in such a way that the disturbance is removed or at least partially 
compensated. The disturbance can be removed by connecting a reserve 
component. Routine maintenance measures (for example, calibration) are 
carried out according to a fixed time program, whereby faults which may 
occur are identified in the form of failure indications.

DETAILED DESCRIPTION OF THE INVENTION 
According to FIG. 1 test gas is removed from an operating line by a probe 1 
(extraction device) and conveyed through a test gas condenser 2. The 
condensate produced can be discharged by means of a valve 3. The test gas 
is subsequently dried in an absorber 4a, whereby a reserve absorber 4b can 
be connected with the aid of a valve 5. A pump 6 conveys the test gas 
through a flow meter 7 and to analysis instruments 8a, 8b which are rinsed 
by a protective gas whose flow is checked by a flow meter 9. The test gas 
condenser 2 and absorber 4a and 4b form the processing chain connected 
upstream of the analysis instruments 8a and 8b and their measured value 
display 12. The first analysis instrument 8a should have a thermostat 18 
and the second 8b a status display 10. By using a valve combination 11, it 
is possible to convey search gases (null or sensitivity gas) through the 
analysis instruments instead of test gas. The measured values in the 
analysis instruments are displayed on a recorder 12 and registered. Zero 
and sensitivity can be adjusted by potentiometers 13a, 13b. 
This measuring device is equipped with the following status sensors: 
thermometers 14 for test gas condenser temperature; sensors 15a, 15b for 
the condition of the absorbers; minimal contacts 16, 17 on the flowmeters 
7, 9; thermometer 18 for analysis instrument temperature control, status 
display 10 on the analysis instrument 8b. All status sensors are connected 
to a central monitoring unit U. Unlike the known instruments, it is 
coupled to the processing chain and the analysis instruments in a type of 
shunt. This prevents the data flow from the analysis instruments 8a, 8b to 
the measured value display 12 from being obstructed. Moreover, the 
monitoring unit can, in passing, be disconnected from the measuring device 
in this way without impairing the fundamental operation of the analysis 
measuring device. The monitoring unit U receives other information 
directly from the measured values (lines 30, 31). 
The monitoring unit U can connect all valves which shift adjusting 
potentiometers and disconnect the current supplies of the test gas 
condenser and the thermostat with relays 19, 20. The condition of these 
outputs is displayed on the monitoring unit by light-emitting diodes 21. 
The valves can also be controlled manually by switches 22. 
A total of seven internally adjustable voltages 23 allows the monitoring 
unit U to be adapted to a variety of measuring devices. The desired values 
for the zero point and sensitivity adjustments of the analysis 
instruments, the permitted variation in the measured values and the lower 
limit to the measuring range (for checking plausibility) can be selected 
at random. When monitoring the temperature, the upper limit of the 
permitted temperature range can be predetermined, the monitoring unit U 
ascertaining from the magnitude of these limit values whether a condenser 
or a thermostat is to be checked. Voltage supplies can be disconnected 
accordingly, depending on whether under-cooling or over-heating is 
established. The desired values for the sensitivity adjustments similarly 
indicate how many analysis instruments are to be monitored and calibrated. 
Disturbances are indicated internally in different ways, depending on their 
cause, by light-emitting diodes 24. External failure indications are 
emitted overall in two stages ("warning" "measurement absent") in the form 
of potential-free contacts 25. Two other externally usable messages 26 
identify the operating condition of the measuring device. "Calibration" is 
indicated if the measuring device is occupied with itself and the measured 
values are not available. "Maintenance" is indicated if the maintenance 
switch 27 is pressed. If that is so, the measuring device runs by manual 
operation, i.e. the monitoring unit is disconnected from the rest of the 
measuring device. All externally usable messages are represented 
internally by light-emitting diodes 28. 
A micro-processor which jumps to the beginning of the program fed into it 
upon actuation of switch 29, is contained as a central component in the 
monitoring unit U. 
FIG. 2 shows the functioning of the monitoring unit in the form of a flow 
chart. 
Once the voltage has been switched on or the switch 29 actuated (FIG. 1), 
the system jumps from the starting point a to b then examines whether the 
maintenance switch 27 (FIG. 1) is pressed. If this is so, the system 
remains in a maintenance loop c in which the monitoring unit is 
disconnected and the rest of the measuring device situated in its basic 
condition. If the maintenance switch is not pressed, the system remains in 
maintenance loop d until the temperatures to be monitored lie within the 
desired range. In the next portion e, an examination is made to see 
whether the status display of the analysis instrument 8b, FIG. 1, signals 
disturbance-free operation uninterruptedly for at least 15 seconds. 
The portion "adjust sensitivities" f follows. The analysis instruments are 
traversed in succession with sensitivity gas (gas of known concentration) 
with the aid of the valve combination 11. After a rinsing period, the 
flowmeter 7 and its minimum contact 16 are used to check whether 
sensitivity gas is flowing through the analysis instruments. If not, 
failure indications are emitted. If so, the measured value of the analysis 
instrument to be adjusted is brought step-wise to the predetermined 
desired value with the aid of a sensitivity motor potentiometer. If more 
than 32 steps are needed or if the direction of adjustment has to be 
changed more than twice, adjustment is interrupted and failure indications 
are emitted. The zeros are adjusted accordingly in the following portion 
g. 
The measured value is not available during the adjustments. This is 
announced externally by the message "calibration". This message is 
retracted only after sufficiently long rinsing with test gas. 
If the maintenance switch 27 is pressed in portion c, all failure 
indications are cancelled, the rest of the measuring device is shifted 
into its basic condition, and the monitoring unit is disconnected. If the 
maintenance switch is only actuated briefly, the program jumps into the 
portions f and g (calibration). 
A check as to whether the flows are sufficiently large and whether the 
status display of the analysis instrument 8b displays disturbance-free 
operation is carried out in portion h. A check is carried out in portion i 
as to whether the temperatures of the test gas condenser and the 
thermostat of the analysis instrument 8a lie in the desired range. If the 
desired range is fallen below or exceeded, the voltage supplies are 
disconnected. If the thermostat temperature does not lie in the desired 
range, adjustments are made hourly to compensate zero and sensitivity 
drifts. 
The condition of the absorbers 4a and 4b is examined in portion j. If the 
absorber 4a is exhausted, the reserve absorber 4b is connected by the 
solenoid valve 5. If both absorbers are exhausted, the test gas is 
disconnected to protect the analysis instrument. 
The plausibility of the test values is examined in portion k. If they lie 
outside the measuring range or their variation exceeds that allowed by a 
predetermined range of variation, messages are emitted, as in the case of 
all other disturbances. Depending on the effect of a failure on the 
measured values, "warning" or "measurement absent" is indicated 
externally. 
The time interval of the other portions is controlled in the time branches 
1. The program jumps to portion c every 0.1 seconds. A temporal delay is 
incorporated so that variations having frequencies of 10 Hz can be 
detected when examining plausibility. 
The external failure indications are initially cancelled every 10 minutes 
in portion m if they do not originate from portions f or g (calibration). 
They are produced again in the following one if the causes of the failure 
are still present. The external failure indications are thus up-dated. 
Portion n (condensate discharged) with which the condensate produced in the 
test gas condenser is discharged by actuation of the solenoid valve 3 is 
inserted every 24 hours or 168 hours. As the measured values are not 
available in this process, the external output "calibration" is positioned 
during this operation. Portions f and g (calibration) follow n.