I am trying to find either a portable or bench frequency calibrator to be used as an input to a PLC DC input card or device. I am trying to simulate a open collector type pulse signal (flow sensor pulse output into a PLC input). The PLC requires a 14V minimum signal in order to register. The frequency I need needs to be adjustable. Approximately 1-1000 HZ but higher frequency range is fine. The nominal impedence of the PLC input is 3000 Ohms. I have tried to find a vendor with this type of device but the 14 volt minimum seems to be a problem. My application is using a AB Micrologix 1000/1500/or 1746-ITB1. Does anyone know of any frequency calibrators that could do this? Thanks a lot.