This invention relates in general to facsimile systems and in particular, it relates to an internal self-diagnostic circuit for a facsimile transceiver and to a method of testing a facsimile transceiver.
Facsimile systems are systems in which light/dark variations in a document at one location may be detected by one transceiver and converted into amplitude modulated or frequency modulated signals for transmission to a transceiver at a remote location where these signals are translated back to light/dark variations on a document. Many factors may affect and degrade the copy quality at the remote location. Some degradation in copy quality may be due to difficulties with the transmission line and some may be due to malfunctions of either the near or the remote transceiver. Therefore, it is desirable for the user of a facsimile transceiver to determine whether degradation in copy quality is caused by his own transceiver or by external factors. It is also desirable for the user of a facsimile transceiver to periodically test his own transceiver regardless of whether copy degradation has been observed in order that routine maintenance may be performed if necessary. In view of these considerations, it is desirable to provide a facsimile transceiver with means for internal diagnosis which is sometimes referred to as a self test mode.
One such prior art internal diagnostic method and apparatus for a facsimile transceiver is disclosed in U.S. Pat. No. 3,937,872 to Kondo et al. In the method and apparatus employed by Kondo et al, both the transmitting and receiving sections of the facsimile transceiver and the reading and writing means are operated simultaneously and the intensity of the light source of the transmitting section is electively varied. The output of the receiving section is then observed for variations in intensity, the reading and writing means being spaced apart some distance from one another. A malfunction of the transceiver is then determined to be present if the light/dark variation produced by the write head does not track the intensity variation induced at the read head.
In another known prior art technique, transmitting and receiving sections of the facsimile transceiver are simultaneously energized with the reading and writing means also operated simultaneously and again being spaced apart by some distance. A document having a test pattern on only a portion thereof is then employed and the read head scans that portion of the document containing the test pattern while the write head (spaced apart therefrom) generates a copy of the test pattern on the same document.
Both of these prior art techniques suffer from the disadvantage that the reading and writing means of the transceiver are operative simultaneously. It has been found that electrical noise from the writing means may affect the reading means thus causing a source of copy degradation not found in a normal operation of the transceiver thus decreasing the validity of these internal diagonstic methods.
Moreover, both the known prior art techniques require the reading and writing means to be physically spaced apart from one another in order that a sufficiently large test pattern area may be read while being simultaneously displayed by the writing means. However, it is generally desirable to keep the design of the reading and writing means compact so as to minimize the overall size of the transceiver. However, when the reading and writing means are closely spaced, the afore-mentioned problem of electrical noise is magnified when both are activated simultaneously.