Photometric process measuring apparatus and method for performing photometric measurements

Abstract

The invention relates to a photometric process measuring device (10) with a photometric immersion probe (20). The photometric immersion probe (20) comprises a photometric flash light source (61) for providing photometric light pulses, a photometric detector device (70) comprising at least two separate wavelength selective detection elements (71, 72, 73), and a photometric controller (80) controlling the photometric flash light source (61) and the detector device (70). The photometer controller (80) comprises a number of pulse signal integrators (819, 829, 839) for integrating electrical pulses generated by the detection elements (71, 72, 73), a number of A / D converters (81, 82, 83) for converting the voltage of the pulse signal integrators (819, 829, 839) when a high precision conversion trigger port (H) of the A / D converters (81, 82, 83) is triggered, and a measurement loop controller (90) having an integration target memory (94) that stores an integration target voltage value (Ut). The photometer controller (80) is provided with a high precision request port (93) for synchronously triggering high precision conversion trigger ports (H) of all A / D converters (81, 82, 83) after the voltage of a first one of all pulse signal integrators (819, 829, 839) has exceeded a stored integration target voltage value (Ut).

Description

Technical Field

[0001] The invention relates to a photometric process measuring device with a photometric immersion probe and a photometric measuring method provided by the photometric process measuring device. Background Art

[0002] A photometric process measuring device comprises a photometric immersion probe which is immersed in water of a water tank. The water tank may be part of a water treatment plant for continuously controlling drinking water or for controlling process steps of a wastewater treatment process. A typical photometric immersion probe is disclosed in DE 10 2005 007 142 A1. The prior art immersion probe comprises a photometric flash lamp source for providing photometric light pulses having a sufficiently continuous or quasi-continuous spectrum and comprises a photometric detector device having a beam splitter and having at least two separate wavelength selective detection elements.

[0003] In the photometric controller of the prior art, the wavelength selective detection element is provided with a pulse signal integrator for integrating the electric pulses generated by the detection element. The pulse signal integrator is a capacitor with a saturation voltage, which cannot be exceeded during the integration process within the measurement cycle, so that the number of integrable flash light source flashes within one measurement cycle is limited. Since the general application environment of the photometric process measurement device can be very clear drinking water as well as highly turbid waste water, the maximum acceptable number of flash light source flashes within one measurement cycle can range from very few flashes for very clear drinking water to more than one hundred flashes for very turbid waste water. Therefore, it is necessary to predefine the number of flashes for avoiding the saturation voltage of the capacitor within the measurement cycle depending on the expected possible water turbidity range of the application. However, in the case of unexpected relatively clear water samples, the saturation voltage of the pulse ignition integrator can be reached and exceeded unintentionally, so that the corresponding result of the measurement cycle cannot be used. This can be avoided by predefining the maximum number of flashes of the measurement cycle to be relatively low, which implies that the accuracy potential of the photometer controller is not utilized. Summary of the invention

[0004] It is an object of the present invention to provide a photometric process measurement device and a method for providing photometric measurements with improved system accuracy.

[0005] This object is achieved by means of a photometric process measuring device having a self-regulated pulse signal integration with the features of the independent device claim 1 and by means of a photometric measuring method with the features of the independent method claim 6 .

[0006] The photometric process measuring device according to the invention is provided with a photometric immersion probe, which is preferably continuously and completely immersed in the water of the pool. The immersion probe comprises a photometric flash light source for providing photometric light pulses with a suitable and sufficiently continuous spectrum, preferably with a spectrum focused in the ultraviolet range for determining, for example, the concentration of nitrates and nitrites. Preferably, the flash light source is a high-pressure gas discharge lamp, more preferably a xenon flash lamp.

[0007] The photometric detector arrangement comprises at least two separate wavelength selective detection elements which may be a combination of a beam splitter, a wavelength selective filter and a photocell, or a suitable arrangement allowing wavelength selective detection of the intensity of at least two discrete wavelengths of the light pulses generated by the flash lamp source after transmission through the water sample. The photocell may be a silicon photocell and the wavelength selective filter may be an interference bandpass filter.

[0008] The photometer controller controls the photometer flash source by triggering each flash source pulse. The photometer controller includes a pulse signal integrator for each detection element for integrating the electrical pulses generated by the corresponding detection element. The pulse signal integrator is preferably a capacitor. The photometer controller includes an A / D converter for converting the voltage of the pulse signal integrator. Each pulse signal integrator is provided with a corresponding A / D converter. Each A / D converter is provided with a high-precision conversion trigger port. If the high-precision conversion trigger port is electronically triggered, a high-precision A / D conversion is started. The A / D conversion with high precision can take, for example, up to 100 milliseconds, so that the high-precision A / D conversion is preferably only acceptable for the final determination of the voltage of the pulse signal integrator at the end of the measurement cycle.

[0009] The photometer controller is provided with a measurement cycle controller having an integration target memory storing an integration target voltage value. The photometer controller is also provided with a high-precision request port and synchronously triggers the high-precision conversion trigger ports of all A / D converters after the voltage of the first one of all pulse signal integrators has exceeded the stored integration target voltage value. Once the voltage of one of all pulse signal integrators has reached the integration target voltage value, the photometer flash light source is stopped and all A / D converters are triggered to read and digitize the voltage of the corresponding pulse signal integrator with maximum available digital resolution and accuracy.

[0010] If the water sample is relatively clear, the number of photometric light pulses generated within a measurement cycle is relatively low. If the water sample is relatively turbid, the number of photometric light pulses within a measurement cycle is relatively high. The total number of photometric light pulses generated by the photometer flash lamp source within one measurement cycle is adjusted according to the turbidity of the sample water.

[0011] This does not necessarily mean that such regulation is implemented for each single measuring cycle. Regulation can be provided flexibly or at fixed intervals, for example, every 20th measuring cycle or once per minute. Other measuring cycles as slave measuring cycles are not regulated individually, but are identical to the regulating measuring cycle as the master measuring cycle. This concept allows to spend more time accurately analyzing the master measuring cycle instead of the subsequent slave measuring cycles, without substantially degrading the overall measuring cycle frequency.

[0012] The flexible adjustment of the length of the measuring cycle allows the capacity of the pulse signal integrator and the A / D converter to be utilized to the greatest possible extent, so that the overall accuracy of the quantitative determination of the substances in the sample water is greatly increased.

[0013] There are generally different technical ways to monitor the development of said voltage of the pulsed signal integrator during a measuring cycle. Preferably, the monitoring is not realized by providing a high-precision A / D conversion after each single flash lamp pulse, since a high-precision A / D conversion is relatively time-consuming and takes more time than the interval between a possible interval between two photometric light pulses. Preferably, no more than five said high-precision A / D conversions are provided within a single measuring cycle. More preferably, said high-precision A / D conversion is not used at all to monitor the development of said voltage of the pulsed signal integrator, but only for the final determination of said voltage of all A / D converters at the end of a measuring cycle.

[0014] Preferably, the photometric controller is provided with an integrator reset switch, which is used to synchronously reset all pulse signal integrators before a new measurement cycle starts. After all A / D converters have converted the final voltage of the pulse signal integrator under high-precision conversion, the integrator reset switch is triggered. The integrator reset switch synchronously pulls down the voltage of all pulse signal integrators to zero, so that a new measurement cycle can be started.

[0015] Preferably, the integration target voltage value is at least 20% lower than the saturation voltage of the pulse signal integrator, but at least 50% of the saturation voltage. For the case of very clear water samples that cause relatively high optical and electrical pulses received by the pulse signal integrator, the integration target voltage value must be substantially lower than the saturation voltage of the pulse signal integrator. The offset between the saturation voltage and the integration target voltage value must be higher than the highest possible pulse signal voltage of a single light pulse received by any of the detection elements.

[0016] Preferably, the photometric controller is provided with a flash counter for counting the number of flashes during a measurement cycle, and is provided with a maximum flash number memory storing the total maximum flash number value of flashes within a single measurement cycle. When the number of flashes counted by the flash counter is equal to or exceeds the stored maximum flash number, the photometric controller triggers the high-precision conversion trigger ports of all A / D converters. The total maximum number of integrated flashes defined within a measurement cycle is a fallback measurement for situations where the sample water is unexpectedly turbid or if other factors unexpectedly significantly weaken the light ultimately received by the wavelength selective detection element. In this case, the measurement cycle is terminated before the voltage usage of any one of the pulse signal integrators has exceeded the stored integration target voltage value. In this case, a warning signal can be generated to cause control and maintenance actions.

[0017] Preferably, the A / D converter is provided with a low-precision conversion trigger port. Preferably, if the voltage of all pulse signal integrators is lower than the stored integral target value, all low-precision conversion trigger ports of all A / D converters can be synchronously triggered by the corresponding low-precision request port of the photometric controller. The low-precision conversion of the A / D converter usually takes only a few milliseconds, so that the low-precision conversion capability of the A / D converter can be used at the beginning and / or during a measurement cycle to provide a prediction of the total number of photometric light pulses within the measurement cycle until the voltage of the first pulse signal integrator of all pulse signal integrators will exceed the stored integral target voltage value. This prediction allows the moment of the relatively time-consuming high-precision A / D conversion to be perfectly scheduled and planned at the end of the measurement cycle.

[0018] The technical minimum interval between two subsequent photometric light pulses generated by the photometer flash lamp source is typically in the range of 10 ms to 30 ms, so that the low-precision conversion interval of a typical A / D converter is shorter than the flash interval and thus does not substantially affect the photometer pulse frequency.

[0019] The method claim according to the invention relates to a photometric measurement method provided by a photometric process measuring device comprising the features of one of the apparatus claims and comprising the following measurement cycle method steps controlled by a photometer controller:

[0020] generating a plurality of light pulses using the photometer flash lamp source,

[0021] monitoring the voltage of all pulse signal integrators of the wavelength selective detection element,

[0022] When the voltage of the first pulse signal integrator among all the pulse signal integrators has exceeded the stored integration target voltage value: synchronously triggering the high-precision conversion trigger ports of all A / D converters to determine the final voltage of all the pulse signal integrators,

[0023] Reset all pulse signal integrators, and

[0024] Starts a new measuring cycle.

[0025] The monitoring of the voltage of the pulse signal integrator can generally be provided in different ways by different means. However, it is preferably not provided by continuously using the high-precision conversion function of the A / D converter, because the high-precision conversion of the A / D converter is very time-consuming and will substantially prolong each measurement cycle.

[0026] Preferably, the monitoring step is provided by the photometer controller by triggering the low precision conversion trigger port of all A / D converters. Since low precision conversion takes only a few milliseconds, the monitoring action using the low precision conversion function of all A / D converters does not substantially affect the length of the measurement cycle.

[0027] Preferably, the photometric controller estimates the total number of flashes of a complete measuring cycle before the fourth flash of the measuring cycle. In other words, a first estimate of the total number of flashes and pulses of a complete measuring cycle is provided very early, so that - even in the case of very clear sample water - it can be reliably avoided that one of the pulse signal integrators is inadvertently charged to the saturation voltage of the signal integrator.

[0028] Preferably, the photometric controller triggers the high-precision conversion trigger ports of all A / D converters and starts a new measurement cycle when the number of flashes within a measurement cycle equals the stored maximum number of flashes. Defining the maximum number of integrated flashes within a measurement cycle avoids too long measurement cycles for situations where the sample water is unexpectedly turbid or if other factors impair the light received by the wavelength selective detection element. In this case, a warning signal can be generated to cause control and maintenance actions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] An embodiment of the present invention is described with reference to the accompanying drawings, in which:

[0030] Figure 1 Schematically shows a photometric process measurement device with a photometric immersion probe comprising a photometric detector arrangement and a photometer controller,

[0031] Figure 2 The schematic diagram in more detail shows Figure 1 a photometric detector device and a photometric controller, and

[0032] Figure 3a to Figure 3d The water absorption and turbidity of different samples are shown Figure 1 and Figure 2 A graph of the voltage versus time of the pulse signal integrator of the photometer controller having the highest received light pulse intensity. DETAILED DESCRIPTION

[0033] Figure 1 Schematically shows a photometric process measuring device 10 which is essentially composed of a land-based control unit 12 and a photometric immersion probe 20 arranged remote from the land-based control unit 12. The immersion probe 20 is arranged below the water surface 18 and is completely immersed in the water 17 of a water tank 16. The water tank 16 may be part of a wastewater treatment plant. Alternatively, the immersion probe 20 may be used in laboratory applications.

[0034] The measuring device 10 is generally suitable for quasi-continuously photometrically determining the concentration of at least one water parameter. In the present exemplary embodiment, the photometric process measuring device 10 determines the concentration of nitrites and nitrates in the sample water 17 with a measuring frequency of a few seconds.

[0035] The photometric immersion probe 20 comprises, within a fluid-tight probe housing 22, an electronic flyback-converter 30 for exciting a pulse energy capacitor 33, comprising a pulse ignition switch 36 and a photometer flash lamp source 61, which is a xenon flash lamp for providing photometric light pulses with a sufficient quasi-continuous spectrum in the ultraviolet range. The flyback converter 30 is supplied with electrical energy by the land-based control unit 12 via a power supply line 52 and comprises a converter switch 31, a transformer 32 and a blocking diode 35. The charging duration for charging a completely empty pulse energy capacitor 33 is about 10 ms until the voltage of the pulse energy capacitor reaches a defined ignition voltage value.

[0036] The photometric immersion probe 20 comprises a photometric detector arrangement 70 having an optical beam splitter 78 and three individual wavelength-selective detection elements 71 , 72 , 73 . Each wavelength selective detection element 71, 72, 73 includes an interference bandpass filter 71', 72', 73' and a corresponding photocell 71", 72", 73". The detection elements 71, 72, 73 detect light pulses at wavelengths of 218 nm, 225 nm and 245 nm generated by the flash lamp source 61. The 218 nm and 225 nm detection elements 71, 72 are used for direct detection of extinction / absorption caused by the nitrite and nitrate concentrations in the detected water. The 245 nm detection element 73 is a reference detector for monitoring the general composition and performance of the flash lamp source 61 and the optical path between the flash lamp source 61 and the detection elements 71, 72, 73. The photometer flash lamp source 60 and the photometric detector device 70 define a photometer device for detecting light absorption of sample water in a photometric measurement section 64, and the photometric measurement section 64 is defined between a measurement section light entrance window 65 and a measurement section light exit window 66.

[0037] The photometric immersion probe 20 includes a photometer controller 80 having: three pulse signal integrators 81', 82', 83'; three corresponding A / D converters 81, 82, 83; an integrator reset switch 86; and a measurement cycle controller 90. The pulse signal integrators 81', 82', 83' are technically capacitor elements and accumulate voltage pulses generated by the photometric detection unit 70 until the integrator reset switch 86 is closed and all pulse signal integrators 81', 82', 83' are discharged. The pulse signal integrators 81', 82', 83' have a saturation voltage Us of, for example, 2600 mV.

[0038] The three A / D converters 81, 82, 83 each have a high-precision conversion trigger port H and a low-precision conversion trigger port L. When the low-precision conversion trigger ports L of the three A / D converters 81, 82, 83 are synchronously triggered, a low-precision A / D conversion of the actual voltage of the three corresponding pulse signal integrators 81', 82', 83' is provided, which only takes about 2 ms. The low-precision conversion takes less time than the charging of the pulse energy capacitor 33.

[0039] When the high-precision conversion trigger ports of the three A / D converters 81, 82, 83 are synchronously triggered, very accurate and high-precision A / D conversion of the actual voltage of the three corresponding pulse signal integrators 81', 82', 83' is provided by the corresponding A / D converters 81, 82, 83, which takes about 65 ms. The high-precision conversion takes more time than the charging of the pulse energy capacitor 33.

[0040] The measurement cycle controller 90 includes a reset port 91 for activating the integrator reset switch 86, a low-precision request port 92 for synchronously requesting fast low-precision A / D conversion via a low-precision conversion trigger port L of the A / D converters 81, 82, and 83, and a high-precision request port 93 for synchronously requesting high-precision A / D conversion via a high-precision conversion trigger port H of the three A / D converters 81, 82, and 83.

[0041] The measuring loop controller 90 further comprises an integrated target memory 94 storing the integrated target voltage value Ut, and comprises an evaluation module 95 for continuously evaluating the digital A / D converter result related to the integrated target voltage value Ut. In the present embodiment, the integrated target voltage value Ut is 2000 mV.

[0042] The measuring cycle controller 90 comprises a flash counter 99 for counting the cyclic flashes F generated by the flash lamp source 61 within one measuring cycle, and comprises a maximum flash number memory 99 ′ storing a maximum flash number Fmax of 64 flashes in this embodiment.

[0043] The measurement cycle controller 90 further includes a signal ramp pattern table memory 96 and a cycle pattern table memory 98 .

[0044] The photometer controller 80 controls the entire measurement process and adjusts the length of the measurement cycle according to the intensity level of the light pulses received by the photometric detection unit 70 and integrated by the pulse signal integrators 81 ′, 82 ′, 83 ′.

[0045] The immersion probe 20 comprises an electronic probe controller 50 for controlling communications between a photometer controller 80 of the immersion probe 20 and control electronics 14 of the land-based control unit 12 via signal lines 51 .

[0046] When the photometer controller 80 starts a new measurement cycle CY, the pulse ignition switch 36 is electronically caused to provide a photometric light pulse with a flash interval of, for example, about 20 ms generated by the photometer flash lamp source 61. After the third single flash, the photometer controller 80 requests a low-precision conversion via the low-precision request port 91 and the connected low-precision conversion trigger port L of all A / D converters 81, 82, 83 after each subsequent single flash, and compares the digital low-precision voltage value U provided by the A / D converters 81, 82, 83 with the stored integrated target voltage value Ut stored in the integrated target memory 94. As long as the highest digital voltage value U of all A / D converters 81, 82, 83 is lower than the stored integrated target voltage value Ut, the measurement cycle CY is continued by continuing the flash action.

[0047] Once the voltage U of the first pulse signal integrator among all the pulse signal integrators 81', 82', 83' has exceeded the stored integrated target voltage value Ut, the flashing action is stopped, and the photometer controller 80 requests synchronized high-precision A / D conversion via the high-precision request port 93 and the corresponding high-precision conversion trigger ports H of all A / D converters 81, 82, 83 to determine the final digital voltage values ​​of all pulse signal integrators 81', 82', 83'. These final digital voltage values ​​are then converted into corresponding concentration values ​​of nitrite and nitrate in the sample water 17, and into corresponding device condition values. After the high-precision conversion, the reset port 91 of the measurement cycle controller 90 prompts the integrator reset switch 86 to reset the pulse signal integrators 81', 82', 83' to be reset to a zero voltage value, so that the photometer is ready for the next measurement cycle.

[0048] Figure 3a to Figure 3d The measurement cycles CY for different sample water absorptions are shown for the detector element receiving the highest light intensity of all three detector elements 71, 72, 73. The pulse time interval ti is always constant and is about 20 ms. The high-precision conversion time interval tc of a single high-precision conversion interval 100 is always constant and is about 65 ms.

[0049] Figure 3a Several identical measurement cycles CY for very clear drinking water causing very low overall light absorption are shown for the detector element receiving the highest light intensity. Therefore, each photometric light pulse causes a relatively high pulse voltage Ui at the corresponding pulse signal integrator 81', 82', 83'. After the third flash light source pulse, the measurement cycle controller 90 receives the integrated low-precision digital voltage value U of the corresponding A / D converter 81, 82, 83, compares the integrated low-precision voltage value U with the stored integrated target voltage value Ut, detects that another photometric light pulse generated by the photometer flash light source 61 is not exceeded and is allowed. After the fourth flash light source pulse, the measurement cycle controller 90 again receives the integrated low-precision voltage value U of the corresponding A / D converter 81, 82, 83, compares the integrated low-precision voltage value U with the stored integrated target voltage value Ut, and detects that the integrated low-precision voltage value U is now higher than the stored integrated target voltage value Ut. The measurement cycle controller 90 now stops the flashing action and causes all A / D converters 81, 82, 83 to provide high-precision conversion with maximum accuracy. After the high-precision conversion has been completed, the integrator reset switch 86 is closed to synchronously reset and fully discharge all pulse signal integrators 81', 82', 83' so that a new measurement cycle CY can be started continuously.

[0050] Figure 3b and Figure 3c A measuring cycle CY of a more turbid sample water is shown which results in a less intense individual pulse voltage Ui and in a correspondingly longer measuring cycle CY.

[0051] Figure 3d Finally, a measurement cycle of a very turbid water sample with a very low single pulse voltage Ui is shown. As soon as the flash counter 99 indicates that the number of flashes F within one measurement cycle CY is equal to the maximum number of flashes Fmax 64 stored in the maximum number of flashes memory 99', the measurement cycle CY is completed by causing all A / D converters 81, 82, 83 to provide high-precision conversions and the measurement cycle CY is ended.

[0052] Typically, after the first few flashes, the measurement cycle controller 90 can provide an estimate of the expected number of photometric light pulses until the first of the pulse signal integrators 81', 82', 83' reaches the integrated target voltage value Ut, so that the measurement cycle controller 90 does not need to continuously control the actual progression of the voltage of the pulse signal integrators 81', 82', 83'.

Claims

1. A photometric process measuring device (10), the photometric process measuring device having a photometric immersion probe (20), the photometric immersion probe comprising: A photometer flash lamp source (61) for providing photometric light pulses, A photometric detector arrangement (70) comprising at least two separate wavelength selective detection elements (71, 72, 73), and a photometer controller (80) which controls the photometer flash light source (61) and the photometer detector device (70), The photometer controller (80) comprises: a pulse signal integrator (81', 82', 83'), wherein the pulse signal integrator is used to integrate the electrical pulses generated by the detection elements (71, 72, 73), A / D converters (81, 82, 83) for converting the voltage of the pulse signal integrators (81', 82', 83') when the high-precision conversion trigger port (H) of the A / D converters (81, 82, 83) is triggered, and A measuring loop controller (90) having an integral target memory (94) for storing an integral target voltage value (Ut), The photometer controller (80) is provided with a high-precision request port (93), which is used to synchronously trigger the high-precision conversion trigger ports (H) of all A / D converters (81, 82, 83) after the voltage of the first pulse signal integrator among all pulse signal integrators (81', 82', 83') has exceeded the stored integration target voltage value (Ut).

2. The photometric process measuring device (10) according to claim 1, wherein: The A / D converters (81, 82, 83) are respectively provided with low-precision conversion trigger ports (L), and if the voltages of all pulse signal integrators (81', 82', 83') are lower than the stored integration target value (Ut), the low-precision conversion trigger ports (L) are synchronously triggered by the corresponding low-precision request ports (92) of the photometer controller (80).

3. The photometric process measuring device (10) according to one of the preceding claims, wherein: The photometer controller (80) is provided with a flash counter (99) for counting the number of flashes (F) of a measurement cycle and is provided with a maximum flash number memory (99') for storing a maximum flash number (Fmax) of a measurement cycle, and when the number of flashes (F) counted by the flash counter (99) is equal to the maximum flash number (Fmax), the photometer controller (80) triggers the high-precision conversion trigger ports (H) of all A / D converters (81, 82, 83).

4. The photometric process measuring device (10) according to one of the preceding claims, wherein: The photometric controller (80) is provided with an integrator reset switch (86), which is used to synchronously reset all pulse signal integrators (81', 82', 83') before a new measurement cycle begins.

5. The photometric process measuring device (10) according to one of the preceding claims, wherein: The integrated target voltage value (Ut) is at least 20% lower than the saturation voltage (Us) of the pulse signal integrator (81', 82', 83').

6. A photometric measurement method provided by a photometric process measuring device (10) having the features of one of the preceding claims, comprising the following measurement cycle method steps controlled by a photometer controller (80): generating light pulses using the photometer flash lamp source (61), an integrator (81', 82', 83') for monitoring all pulse signals of the wavelength selective detection elements (71, 72, 73), When the voltage of the first pulse signal integrator among all the pulse signal integrators (81', 82', 83') exceeds the stored integration target voltage value (Ut): Synchronously trigger the high-precision conversion trigger port (H) of all A / D converters (81, 82, 83) to determine the final voltage of all pulse signal integrators (81', 82', 83'), Reset all pulse signal integrators (81', 82', 83'), and Starts a new measuring cycle.

7. The photometric method according to claim 6, wherein: The monitoring step is provided by the photometer controller (80) by triggering the low precision conversion trigger ports (L) of all A / D converters (81, 82, 83).

8. The photometric method according to claim 7, wherein: The photometric controller (80) schedules the total number of flashes (Ft) of a complete measurement cycle before the fourth flash of the measurement cycle.

9. Photometric method according to one of the preceding method claims, wherein: The photometer controller (80) triggers the high-precision conversion trigger ports (H) of all A / D converters (81, 82, 83), and when the number of flashes (F) of a measurement cycle is equal to the maximum number of flashes (Fmax), the photometer controller starts a new measurement cycle.

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