JPS588751B2 - Humidity sensor failure detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to failure detection of a humidity sensor, and more particularly to a humidity sensor failure detector having a heater for cleaning the humidity sensor.

Humidity sensors using ceramic or other humidity-sensitive resistors are
Since its properties change significantly due to surface contamination, the attached cleaning heater heats and burns off contaminants such as dust adhering to the surface at regular intervals to keep the surface clean.

In such a humidity sensor, for example, if the heater has a disconnection failure, cleaning is virtually not performed at all, which is extremely inconvenient for automatic humidity measurement.

The same situation applies to other failures; for example, if this is used as a humidity sensor for a humidity regulator, the humidity regulator will malfunction.

In view of the above-mentioned conventional drawbacks, the present invention aims to effectively detect failures in humidity sensors.More specifically, it is an object of the present invention to detect failures during cleaning at a predetermined timing. It is something to do.

FIG. 1 is a block diagram of a humidity sensor failure detector according to an embodiment of the present invention.

Reference numeral 1 denotes a humidity sensor body, which is composed of a humidity-sensitive resistor.

Normally, an AC voltage is applied to the humidity sensor 1 to avoid electrolysis and polarization, but if the AC signal is used as it is, signal processing becomes complicated, so a DC signal is converted to the Ho
Convert to .

The level Ho of this DC signal corresponds to the humidity detected by the humidity sensor 1.

In a normal humidity-sensitive resistor, the resistance value decreases as the humidity increases, and the DC signal level Ho also increases accordingly.

When the sensor is heated by the cleaning operation, the humidity-sensitive resistor exhibits thermistor characteristics, the resistance value becomes one order or more smaller than the resistance value during normal humidity detection, and the DC signal level Ho becomes extremely high.

The level detecting means 3 compares this with the cleaning completion level CE given by the cleaning completion level setter 6, and outputs the result as C.

4 outputs a signal A to drive the cleaning heater 5 at regular time intervals at a predetermined timing, limits the maximum cleaning time, and also outputs short pulses B and B at the start of cleaning and just before reaching the maximum cleaning time, respectively. This is a cleaning timing control means that outputs as '.

If the humidity sensor 1 is normal, the signal CE is given as a reference to the level detection means 3 by the completion level setter 6 at the same time as cleaning starts.

If the cleaning is completed and the resistance value of the humidity sensor 1 is reduced to a predetermined value, the output signal C of the level detection means 3 will be output, and an "AND" gate will be output, and the timing control means 4 will be output. The cleaning signal A is output again after a predetermined period of time has elapsed.

If the humidity sensor has a short-circuit failure, the following will occur.

Note that FIG. 2A shows a timing chart at that time, and the explanation will be made with reference to this figure.

When a short circuit occurs in the sensor, the cleaning signal A
is output at time t0, and at the same time, short-time pulse B is also output.

At this time, a cleaning completion level (CE) is given to one of the level detection means, but because the humidity sensor 1 is short-circuited, the output Ho of the rectifier circuit 2 is at the highest level.
The immediate level detection means outputs C.

That is, in order to heat and clean the humidity sensor 1 with the heater 5, it takes a minimum amount of time after the heater 5 is energized, and the output C of the level detection means is output within a time shorter than that time. This means that the resistance value of the humidity sensor 1 was already small, and this is not a sign of anything other than a malfunction.

Therefore, when the signals C and B are logically multiplied by the "AND" gate 7, the output D is produced, and this data is passed through the "OR" gate 10, latched by the latch 11, and the fault output F
Output.

Next, if the humidity sensor 1 or heater 5 has an open failure,
The resistance value of the humidity sensor 1 does not change and does not exhibit thermistor characteristics.

A timing chart in this case is shown at the beginning of Figure 2.

That is, a short time pulse B' is outputted from the timing control means 4 at time t immediately before the longest time required for cleaning.

Since the resistance value of the humidity sensor 1 remains large, the output C of the level detection stage 3 is not output.

This signal is inverted by INVERTER “gate 8”
When the signal B' is ANDed with the signal B' by the AND gate 9, the output D' is obtained, and this data is passed through the OR gate 10 and latched by the latch 11 to provide the fault output F.

Here, “AND” gates 7, 9, // O R “gate 1”
- gate 10, "INVERTER" gate 8, latch 11
constitutes a failure determination means for outputting a failure signal F based on the logical relationship of each signal.

As explained above, according to the present invention, malfunctions can be detected accurately, making it possible to prevent malfunctions of, for example, hygrometers, humidity regulators, etc. that use humidity sensors, which has a great effect. .

In this embodiment, an alternating current voltage is applied to the humidity sensor 1, but if the sensor does not become abnormal even if a direct current is applied, a direct current may be applied, and in this case, the rectifier circuit 2 can be omitted.

In addition, the signal Hτ increases as the humidity increases, but even if the signal level Ho decreases when the humidity increases, the output format of the level detection means 3 can be appropriately selected. , the same effects as in this embodiment can be obtained.

Further, the timing control means 4, various gates, latches, etc. can be easily realized by a microcomputer, but of course this is in accordance with the gist of the present invention.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is an operation timing chart of FIG. 1. 1... Humidity sensor, 4... Timing control means, 5... Cleaning heater.

Claims (1)

[Claims] 1. A cleaning timing control means for cleaning a humidity sensor having a cleaning heater at a predetermined timing, a level detection means responsive to the output of the cleaning humidity sensor, and an output of the cleaning timing control means and the level detection means. What is claimed is: 1. A humidity sensor failure detector comprising: failure determination means for outputting a failure signal based on the logical relationship.