CAMAC POWER SUPPLY MONITOR MODULE

GENERAL OPERATION:

The single-width CAMAC monitor module obtains its power from the crate which it is monitoring. A general understanding of how the monitor module operates can be obtained from Figure 1. The input +24 and +6 voltage sources are used to generate a +5V nominal power source and a +2.5V nominal reference for use in the module's monitor and internal test circuits. Similarly, the input -24 and -6 volt sources are used to develop a -5v power source and a -2.5 volt reference. The voltage conditioner circuits shown in Figure 1 operate in such a manner that the +/-5 and +/-2.5 voltages are available even if one of the positive input sources and one of the negative input sources fail completely. One monitor circuit is used to watch each of the four input source voltages. Each of the monitor circuits is essentially identical. A typical monitor circuit has an input divide circuit which has a O.OOOV output when the source voltage is exactly equal to its nominal value. If the source voltage changes by +/-1%, the divider output changes by +/-17.6mV correspondingly. A non-inverting amplifier with a gain of 140 increases the divider output swing to +2.5V for a source change of +/-1%. A window comparator, with a threshold of +/-2.5V produces a TTL compatible low output signal whenever the source voltage exceeds +/-1% of its nominal value. A low comparator output drives a ohe-second re-triggerable ohe-shot Which causes a status LED to light, indicating that the corresponding source voltage is "out-of-tolerance". The one-shot circuit is connected in such a way that the LED remains on one second longer than the source voltage is out-of-tolerance. The output of the comparator is ANDed with the other three monitor circuit outputs to produce an open-collector output signal that indicates one of the crate voltages is "out-of-tolerance". The open collector output is for use as part of a daisy-chain alarm system. In addition to the four source monitors, there is a "power-off monitor", which insures that the open collector alarm signal is always correct, even when the CAMAC crate is off. Typical operating ranges for the monitor circuits are given in the next section.

The CAMAC monitor module has an internal test circuit which allows all of the monitor circuits to be checked simultaneously. By means of a front panel switch, a plus and minus 1.2% error sig- nal can be applied to all of the monitor circuits. Under these conditions, all of the status LED's should be "ON' indicating that a similar change in the source voltages would cause the monitor module to indicate an "out-of-tolerance" CAMAC power supply. (A 1.2% test signal is used to insure that the test circuit is useful over a wide range of operating conditions). As an additional diagnostic aid, the +24 and +6 volt source voltages are brought to monitor points on the front panel through 1K Ohm isolating resistors.

CIRCUIT PERFORMANCE AND FEATURES: In order for the monitor modules to operate without frequent adjustments, the reference voltages, monitor divider ratios and amplifiers, shown in Figure 2, must have adequate long term stability and temperature coefficients. To realize good stability, an AD580M reference with 2.500V +/-1% output was chosen. The long term stability of this reference is 100 ppm, and the maximum tempco is 10 ppm/'C. Thus for a 10'C change in temperature, the reference could change by .25mV which would result in a 1.00% error in a 17.6mV monitor divider circuit output signal. The amplifier chosen for the divider output has a maximum tempco of 20uV/'C. This corresponds to an equivalent error of .2mV or 1.13% in a 17.6mV divider output signal for a temperature change of 10'C. The most important single factor in the circuit stability is the resistor chain used in the divider networks. The divider resistors which are used have a maximum tempco of +/-10 ppm/OC and a yearly stability of 25 ppm. Thus under worst conditions, the maximum change in a 17.6 mv signal at the divider output for a 10'C temperature change would be .35mV or 2%. If all of the above factors are considered, the worst condition change or error in a 17.6mV divider output signal would be 4.13% for AT = lO'C. Since the divider output is amplified and compared to a reference signal to establish the alarm for "out of tolerance" power supplies, the alarm trip setting could vary by as much as .413%/'C about the nominal alarm trip setting, i.e., a + 4.13% change in the alarm trip setting would correspond to an alarm trip at +/-1.041% of the nominal power supply voltage.