Exposure time control circuit troubleshooting

1 fault phenomenon

Siemens TRIDOROS 712 MP X-ray machine has a short exposure time and insufficient output when the mAs is greater than 100mAs.

2 Troubleshooting

The first thing to check is if the mAs code is correct. First check the console display, found that when mAs + or mAs-button press the mAs display can become larger or smaller; then check the D3 board mAs code changes are also normal, so that the mAs code sent right. Focus on the timing control circuit D9 and D6 2 board, D9 board is the exposure time controller, D6 board is the limit mAs generator. From the circuit analysis of the D9 board, it can be seen that when the mAs mode is exposed, the tube current is converted into a voltage (-1V=lOOmA) and amplified by the preamplifier J17 and then the main amplifier J15. The mAs code controls the on/off of the analog switch, changing the ratio of the input resistance and the output resistance of the amplifier J15, thus changing the benefits to achieve controlled exposure time. The mAs of the aircraft have 32 steps, corresponding to J15 has 32 different magnifications. coefficient. The signal is amplified by J15 and sent to the integrator J13. The output of the integrator is sent to the follower J12. After the signal arrives from J12, it reaches the comparator J14 and finally triggers the RS trigger. In this way, when the exposure starts, a signal is sent from Z22 to trigger the RS flip-flop, and the flip-flop is reversed. When the integrated voltage reaches +5V, the comparator J14 reverses and the RS flip-flop is reset (RE-SET). Exposure ends. The RS trigger RESET signal is also coming from the D28 of the D9 board. This signal is sent from the Z26 of the D6 board. The role of the D6 board is to set a limit for exposure. This limit is 10% greater than the selected mAs. The working principle of the D6 board is similar to that of the D9. The mAs code is also used to change the gain of the amplifier, but the value of the comparator is slightly higher than that of the D9 board. During the exposure, the D9 board is shut off by the D6 board when it is exposed continuously, which serves as a double insurance.

From the exposure time control process analysis, the aircraft failure is that the exposure is turned off before the mAs is greater than 100mAs, to determine the shutdown signal is sent out from that board? Check the maintenance board D109 board, the board has 3 green lights V29, V30, V31, if it is V29 light during exposure, it means mAs mode exposure, it can be said that the shutdown signal is generated by the D9 board; V30 is off for the dedicated machine time; V31 light indicates that the exposure is off by the D6 board . When the mAs were found to be exposed within 100mAs (including 100mAs), only the V29 lamp was on. When the mAs was greater than 100mAs, both the V29 and V31 lamps were on at the same time during the exposure. It can be concluded that the advance shutdown signal was sent out from the D6 board. Check the D6 board.

There are four digits of mAs coded in, namely B12(20), B20(21), B8(22), and Z8(23), which are analyzed from the coding table and change within 20-100mAs. The encoding of Z8 remains unchanged ( Low level), the other 3 bits are changing, and the exposure is normal, indicating that the circuit related to these 3 circuits is normal. When the mAs is 125 mAs (including 125 mAs) or more, the exposure becomes problematic after Z8 becomes high. The circuit J1 and J2 related to the Z8 should be critically suspected and the logical change of the J1 measurement is correct. Since J2 is an analog switch, it is not good to measure, and an alternative method is used to replace one J2, and the aircraft returns to normal.

Reproduced from the medical device industry