LM1042

`Selectable thermal-resistance or linear probe inputs
`Control circuitry for thermal-resistive probe
` Single-shot or repeating measurements
`Switch on reset and delay to avoid transients
`Output amplifier with 10 mA source and sink capability
` Short or open probe detection
`+50V transient protection on supply and control input
`7.5V to 18V supply range
` Internally regulated supply
` -40 to +80 operation

A typical automotive application circuit is shown in Figure 11 where the probe selection signal is obtained from the oil pressure switch. At power up (ignition on) the oil pressure switch is closed and pin 8 is held low by R4 causing a probe 1 (oil level) measurement to be made. Once the engine has started the oil pressure switch opens and D1 pulls pin 8 high changing over to the second auxiliary probe input.

The capacitor C5 holds pin 8 high in the event of a stalled engine so that a second probe 1 measurement can not occur in disturbed oil. Non-automotive applications may drive pin 8 directly with a logic signal.

The LM1042 uses the thermal-resistive probe technique to measure the level of non-flammable fluids. An output is provided proportional to fluid level and single shot or repeating measurements may be made. All supervisory requirements to control the thermal-resistive probe, including short and open circuit probe detection, are incorporated within the device. A second linear input for alternative sensor signals may also be selected.