(a) The commissioners court of a county may establish a petty cash fund for the sheriff's department in an amount set by the commissioners court. The court shall appropriate the amount from the general fund of the county.
(b) Unless otherwise authorized by a resolution of the commissioners court, the petty cash fund may be used only to advance funds to an officer or employee of the sheriff's department who is required to travel outside the county to conduct an investigation or to obtain custody of a prisoner.