How can I capture PHP Errors and display in the logs?

I have some php code that sometimes errors out. The messages in the logs are very generic and don't help me troubleshoot the problems. I would like to put a more readable and useful error message in the logs. Are there any examples, code snippets, or articles of how I can capture an error condition in the php script and substitute my own message in the logs or pass some variables to the logs?

Thank you,
mlcc2000