I have done quite a bit of proportional and servo control with the Triangle PLC's. The analog outputs on the plc only output 0-5vdc or 0-20ma, not the full 0 to +/-10vdc or current commands typically used on hydraulic servo and prop valves., I have gotten around this by using signal conditioners. Some proportional valve amplifier cards aloow you to bias the input voltage to get a full +/-output to the proportional coil(s).