Checking Contacts; Checking The Fetal Monitor; Rf Problems; Carrier To Noise Ratio - Philips Avalon CTS M2720A Service Manual

Checking Contacts

Checking Contacts
If the transducer cannot be registered to the base station, or you suspect that the transducer is not behaving
normally while it is docked, check that the spring-loaded charge/communication contacts are clean and free
of dirt and ultrasound gel. Check that the springs function correctly by applying pressure with a finger on
the contacts. The contacts should offer some resistance, deflect and return to their normal position; if they
do not, then the top cover should be renewed (see "Replacing the Top Cover Assembly" on page 21).

Checking the Fetal Monitor

If parameter measurements are not possible, first check that the system is connected correctly to the fetal
monitor using the appropriate interface cable as described in the technical specifications. Is the mode
annotated on the recorder trace, or does it appear on the displays? If not, check that the interface cable is
properly connected and that the cable locks are securely fastened. Also ensure that the fetal monitor's
recorder is switched on, and check, and if necessary replace, the power cord.

RF Problems

An RF problem can be summarized as a loss of monitoring capability due to signal corruption in the RF
link (transmitter to antenna to receiver). A lack of parameter measurements, or the inability of the
transducer to reach the registered, ready state may indicate an RF-related problem. A problem is likely to be
an RF problem if it causes any of the following conditions:
• Weak or intermittent signals, or signal loss (see also "Area of Reach" on page 66).
• Interference (see also "RF Interference" on page 68).
The most likely reason for RF problems is a missing or inoperative antenna. Check that it is properly
connected to the base station. If the antenna is properly connected, and the problem persists, then follow
the RF troubleshooting operations in this chapter, starting at "Gathering Data" on page 66 through
"Transducers with Fixed Frequency" on page 71.

Carrier to Noise Ratio

At any time, the performance of the RF reception of a cordless system is dependent on two factors:
– The signal strength of the desired or "carrier" signal.
– The power level of any background RF activity or "noise" at the same frequency.
In order for the cordless system to receive the RF signal without errors (corrupted or invalid data) the
carrier power level must be significantly above the power level of any background noise. If data corruption
occurs, it indicates that at that time the carrier to noise ratio (CNR) was too low.
When RF data corruption occurs, the most obvious symptoms are signal loss, degradation of the area of
reach, or US noise.
The CNR can drop below the critical level for one or both of the following reasons:
• Low signal - the signal strength of the carrier is lower than expected.
• Interference - the background noise level at the receiver frequency is higher than expected.
Ultimately, all of the RF problems within your system occur because of these reasons.
7 Troubleshooting
65