Sample-background-signal autocancellation in fluid-sample analyzers, using symmetrical time-delay or time-averaging

A system for monitoring a first constituent in a fluid stream, which stream may also include a second constituent whose concentration in the stream changes slowly relative to the changes in concentration of the first constituent, comprising:

• a monitoring station, having sensing means for deriving a first component of a first measurement signal in quantitative response to presence of such first constituent in the station;
• said sensing means also deriving an additional component of such first measurement signal in quantitative response to presence of such second constituent in the station, such additional signal component constituting a spurious signal component;
• flow means, connected to the fluid stream and the monitoring station, for directing fluid from the fluid stream through the station;
• primary signal-processing means, connected to receive the first measurement signal from the sensing means, for deriving in response to the first measurement signal a second measurement signal which has a first component and an additional component corresponding respectively to the first and additional components of the first measurement signal, the said primary signal-processing means comprising:
• a signal-averaging device, connected to receive the first measurement signal from the sensing means, for generating the time-average of the first measurement signal over a time interval of specified length to produce the second measurement signal, the said time interval being substantially consistent and not directly controlled by any of the signals;
• secondary signal-processing means, connected to receive the first measurement signal along a signal path from the sensing means and the second measurement signal from the primary processing means, for deriving in response thereto a third signal which is substantially proportional to the difference between the first and second measurement signals, so as to effect substantially complete mutual cancellation of the said additional measurement signal components, whereby the third signal comprises substantially only components corresponding to presence of the first constituent in the stream;
• time delay means, connected in the said signal path between the sensing means and the secondary signal-processing means, for causing the first measurement signal to be delayed in passing along said signal path to the secondary signal-processing means, the length of the delay being less than the said time interval over which the first measurement signal is time-averaged in the primary signal-processing means;
• whereby the secondary signal-processing means in effect combine the first measurement signal with a time-average second measurement signal which is averaged over a time interval partly delayed and partly advanced relative to the effective time of the first measurement signal;
• and
• utilization means responding to the third signal.

A system for monitoring a first constituent in a fluid stream, which stream may also include a second constituent whose concentration in the stream changes slowly relative to the changes in concentration of the first constituent, comprising:

• a monitoring station, having sensing means for deriving, in quantitative response to presence of such constituents in the station, a first measurement signal which is the resultant of a first signal component due to said first constituent and an additional signal component due to said second constituent, the signal component due to the first constituent being desired and that due to the second constituent being spurious;
• flow means, connected to the fluid stream and the monitoring station, for directing fluid from the fluid stream through the station;
• primary signal-processing means, connected to receive the first measurement signal from the sensing means, for deriving in response to the first measurement signal a second measurement signal which is a time-distorted version of the first measurement signal and which has a first component and an additional component corresponding respectively to the first and additional components of the first measurement signal;
• the primary signal-processing means introducing into the second measurement signal a time-distortion which is a substantially consistently applied function of time;
• said function being not directly controlled by any of the signals, and said function having associated with it a characteristic time interval;
• signal-delay means, connected to receive the first measurement signal from the sensing means, for deriving in response to the first measurement signal a third measurement signal which is a delayed version of the first measurement signal and which has a first component and an additional component corresponding respectively to the first and additional components of the first measurement signal;
• the signal-delay means introducing into the third measurement signal a time delay which is partway between zero and the said characteristic time interval;
• secondary signal-processing means, connected to receive the second measurement signal along a signal path from the primary signal-processing means and the third measurement signal along a signal path from the signal-delay means, for deriving in response thereto a fourth signal which is a substantially continuous mathematical function of the second and third measurement signals, the function being such as to effect substantially complete mutual cancellation of the said additional measurement signal components, whereby the fourth signal comprises substantially only components corresponding to presence of the first constituent in the stream;
• and
• utilization means responding to the fourth signal.

A system for monitoring a first constituent in a fluid stream, which stream may also include a second constituent whose concentration in the stream changes slowly relative to the changes in concentration of the first constituent, comprising:

• a monitoring station, having sensing means for deriving, in quantitative response to presence of such constituents in the station, a first measurement signal which is the resultant of a first signal component due to said first constituent and an additional signal component due to said second constituent, the signal component due to the first constituent being desired and that due to the second constituent being spurious;
• flow means, connected to the fluid stream and the monitoring station;
• for directing fluid from the fluid stream through the station;
• primary signal-processing means, connected to receive the first measurement signal from the sensing means, for deriving at each moment during system operation a second measurement signal by additive combination of a plurality of samples of the first measurement signal taken at a plurality of moments during a time interval;
• whereby the second measurement signal has a first component and an additional component corresponding respectively to the first and additional components of the first measurement signal;
• each of the two endpoints of said time interval being one of said plurality of moments;
• and the distribution in time of said plurality of moments at which said samples are taken bearing a substantially consistent relationship to the corresponding moment at which the corresponding second measurement signal is derived, said relationship being not directly controlled by any of the signals;
• signal-delay means, connected to receive the first measurement signal from the sensing means, for deriving in response thereto a third measurement signal by sampling the first measurement signal at a moment which is partway between the said endpoints;
• whereby the third measurement signal has a first component and an additional component corresponding respectively to the first and additional components of the first measurement signal;
• secondary signal-processing means, connected to receive the second measurement signal along a signal path from the primary signal-processing means and the third measurement signal along a signal path from the signal-delay means, for deriving in response thereto a fourth signal which is a substantially continuous mathematical function of the second and third measurement signals, the function being such as to effect substantially complete mutual cancellation of the said additional measurement signal components, whereby the fourth signal comprises substantially only components corresponding to presence of the first constituent in the stream;
• and
• utilization means responding to the fourth signal.