Chief Constable Ben-Julian Harrington has praised the officers’ bravery.
Meanwhile, Essex Police Federation chairman Steve Martin said: “Despite the severity of the assault our officers demonstrated exceptional courage and professionalism.”
He described the incident as “terrifying” and said it was a “stark reminder” of the dangers officers faced daily.
Mr Martin also praised the “heroism” of a member of the public who helped restrain Diedrick.
A jury found him guilty of causing GBH with intent by majority verdict — of 10 jurors to two — after deliberating for about two days.
Diedrick had already pleaded guilty to assault causing GBH without intent and of possessing a blade in a public place.
He was also charged with two counts of attempted murder, but he was found not guilty of those more serious offences.
Sentencing was fixed for 8 December.