LESS THAN STANDARD SEPARATION BETWEEN 2 ACR ACFT.

Narrative

WE WERE USING AN UNUSUAL TFC PATTERN AT THE TIME DUE TO WX. ACFT NORMALLY ON A DOWNWIND LEG AT 6000' WERE ASSIGNED TO 4000'. I WAS WATCHING THE ACFT ON THE DOWNWIND (BEING WORKED BY AN ADJACENT CTLR) WELL AWARE OF ITS ALT OF 4000'. I HAD A DEP COME OFF OF A XING RWY ASSIGNED TO MAINTAIN 3000' BY THE TWR. IT WAS CLEAR IN MY MIND THAT THE DEP SHOULD REMAIN AT 3000' FOR SEP FROM THE DOWNWIND TFC. HOWEVER; WHEN I RESPONDED TO THE DEP'S INITIAL CALLUP; I TRANSPOSED THE ALT I WAS LOOKING AT ON THE DOWNWIND TFC (BEING 4000') TO THE ALT I ASSIGNED TO THE DEP; PLACING THE ACFT IN CONFLICT. I WAS NOT AWARE OF THE PROB UNTIL THE CTLR NEXT TO ME AND I BOTH NOTICED THE DEP CLBING THROUGH 3400'. AT THE SAME TIME THE PLT OF THE DEP ASKED ME ABOUT THE ALT OF THE TFC PASSING OVERHEAD. I TOLD THE PLT THAT THE OVERHEAD TFC WAS MAINTAINING 4000' AND THAT HE HAD BEEN ASSIGNED 3000'. THE PLT THEN INFORMED ME THAT I HAD ASSIGNED HIM 4000'. I SUBSEQUENTLY ASKED THE SUPVR TO PULL THE TAPE FOR VERIFICATION. THE TAPE REVEALED MY ERROR. EVASIVE ACTION WAS NOT REQUIRED. CONTRIBUTING FACTORS WERE ADVERSE WX; UNUSUAL TFC FLOW; AND MY INATTN TO WHAT I ACTUALLY SAID AND LISTENING TO THE PLT'S READBACK FOR ERRORS. SUPPLEMENTAL INFO FROM ACN 97652: THERE WAS ACR Y ABOVE US AND ON A COLLISION COURSE WITH US. THE COPLT LOWERED THE NOSE AND DSNDED BACK DOWN TO 3300'. OUR HIGHEST ALT WAS 3500'.